Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $158.33   13.739%   $180.083   $180.08   $180.10   $180.10  
  Purchase #2 $138.90   3.827%   $144.2157   $144.22   $144.20   $144.20  
  Purchase #3 $97.72   4.453%   $102.0715   $102.07   $102.05   $102.10  
  Purchase #4 $113.73   5.568%   $120.0625   $120.06   $120.05   $120.10  
  Purchase #5 $121.71   5.673%   $128.6146   $128.61   $128.60   $128.60  
  Purchase #6 $249.31   10.415%   $275.2756   $275.28   $275.30   $275.30  
  Purchase #7 $182.43   6.570%   $194.4157   $194.42   $194.40   $194.40  
  7 purchase totals = $1,062.13       $1,144.7386   $1,144.74   $1,144.70   $1,144.80