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 $151.95   7.732%   $163.6988   $163.70   $163.70   $163.70  
  Purchase #2 $188.76   3.273%   $194.9381   $194.94   $194.95   $194.90  
  Purchase #3 $182.28   7.299%   $195.5846   $195.58   $195.60   $195.60  
  Purchase #4 $215.98   5.804%   $228.5155   $228.52   $228.50   $228.50  
  Purchase #5 $159.58   6.420%   $169.825   $169.83   $169.85   $169.80  
  Purchase #6 $123.80   3.736%   $128.4252   $128.43   $128.45   $128.40  
  Purchase #7 $152.26   11.648%   $169.9952   $170.00   $170.00   $170.00  
  7 purchase totals = $1,174.61       $1,250.9824   $1,251.00   $1,251.05   $1,250.90