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 $66.43   10.663%   $73.5134   $73.51   $73.50   $73.50  
  Purchase #2 $170.91   9.760%   $187.5908   $187.59   $187.60   $187.60  
  Purchase #3 $155.62   8.782%   $169.2865   $169.29   $169.30   $169.30  
  Purchase #4 $109.95   3.751%   $114.0742   $114.07   $114.05   $114.10  
  Purchase #5 $97.53   13.471%   $110.6683   $110.67   $110.65   $110.70  
  Purchase #6 $232.27   12.838%   $262.0888   $262.09   $262.10   $262.10  
  Purchase #7 $101.80   11.361%   $113.3655   $113.37   $113.35   $113.40  
  7 purchase totals = $934.51       $1,030.5875   $1,030.59   $1,030.55   $1,030.70