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 $154.67   9.454%   $169.2925   $169.29   $169.30   $169.30  
  Purchase #2 $66.31   10.679%   $73.3912   $73.39   $73.40   $73.40  
  Purchase #3 $68.60   7.256%   $73.5776   $73.58   $73.60   $73.60  
  Purchase #4 $43.28   7.164%   $46.3806   $46.38   $46.40   $46.40  
  Purchase #5 $210.27   13.561%   $238.7847   $238.78   $238.80   $238.80  
  Purchase #6 $236.29   11.345%   $263.0971   $263.10   $263.10   $263.10  
  Purchase #7 $138.56   6.645%   $147.7673   $147.77   $147.75   $147.80  
  7 purchase totals = $917.98       $1,012.2910   $1,012.29   $1,012.35   $1,012.40