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 $35.32   9.424%   $38.6486   $38.65   $38.65   $38.60  
  Purchase #2 $157.30   7.449%   $169.0173   $169.02   $169.00   $169.00  
  Purchase #3 $225.77   10.433%   $249.3246   $249.32   $249.30   $249.30  
  Purchase #4 $169.28   10.683%   $187.3642   $187.36   $187.35   $187.40  
  Purchase #5 $133.75   12.515%   $150.4888   $150.49   $150.50   $150.50  
  Purchase #6 $210.58   7.604%   $226.5925   $226.59   $226.60   $226.60  
  Purchase #7 $229.89   7.226%   $246.5019   $246.50   $246.50   $246.50  
  7 purchase totals = $1,161.89       $1,267.9379   $1,267.93   $1,267.90   $1,267.90