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 $193.32   10.571%   $213.7559   $213.76   $213.75   $213.80  
  Purchase #2 $89.53   13.611%   $101.7159   $101.72   $101.70   $101.70  
  Purchase #3 $218.61   6.396%   $232.5923   $232.59   $232.60   $232.60  
  Purchase #4 $36.26   13.843%   $41.2795   $41.28   $41.30   $41.30  
  Purchase #5 $118.58   4.566%   $123.9944   $123.99   $124.00   $124.00  
  Purchase #6 $165.66   13.415%   $187.8833   $187.88   $187.90   $187.90  
  Purchase #7 $249.39   10.288%   $275.0472   $275.05   $275.05   $275.00  
  7 purchase totals = $1,071.35       $1,176.2685   $1,176.27   $1,176.30   $1,176.30