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 $112.41   6.451%   $119.6616   $119.66   $119.65   $119.70  
  Purchase #2 $77.73   8.785%   $84.5586   $84.56   $84.55   $84.60  
  Purchase #3 $173.73   4.778%   $182.0308   $182.03   $182.05   $182.00  
  Purchase #4 $235.92   13.819%   $268.5218   $268.52   $268.50   $268.50  
  Purchase #5 $140.78   4.143%   $146.6125   $146.61   $146.60   $146.60  
  Purchase #6 $201.41   9.461%   $220.4654   $220.47   $220.45   $220.50  
  Purchase #7 $243.73   11.743%   $272.3512   $272.35   $272.35   $272.40  
  7 purchase totals = $1,185.71       $1,294.2019   $1,294.20   $1,294.15   $1,294.30