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 $161.95   7.855%   $174.6712   $174.67   $174.65   $174.70  
  Purchase #2 $215.25   11.710%   $240.4558   $240.46   $240.45   $240.50  
  Purchase #3 $206.55   13.290%   $234.0005   $234.00   $234.00   $234.00  
  Purchase #4 $59.69   5.187%   $62.7861   $62.79   $62.80   $62.80  
  Purchase #5 $148.90   12.701%   $167.8118   $167.81   $167.80   $167.80  
  Purchase #6 $244.98   9.779%   $268.9366   $268.94   $268.95   $268.90  
  Purchase #7 $169.36   4.843%   $177.5621   $177.56   $177.55   $177.60  
  7 purchase totals = $1,206.68       $1,326.2241   $1,326.23   $1,326.20   $1,326.30