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 $201.96   10.668%   $223.5051   $223.51   $223.50   $223.50  
  Purchase #2 $23.89   3.378%   $24.697   $24.70   $24.70   $24.70  
  Purchase #3 $247.66   11.802%   $276.8888   $276.89   $276.90   $276.90  
  Purchase #4 $95.26   5.573%   $100.5688   $100.57   $100.55   $100.60  
  Purchase #5 $182.69   6.348%   $194.2872   $194.29   $194.30   $194.30  
  Purchase #6 $166.61   13.634%   $189.3256   $189.33   $189.35   $189.30  
  Purchase #7 $126.33   7.469%   $135.7656   $135.77   $135.75   $135.80  
  7 purchase totals = $1,044.40       $1,145.0381   $1,145.06   $1,145.05   $1,145.10