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 $217.44   8.840%   $236.6617   $236.66   $236.65   $236.70  
  Purchase #2 $59.93   12.221%   $67.254   $67.25   $67.25   $67.30  
  Purchase #3 $148.52   13.431%   $168.4677   $168.47   $168.45   $168.50  
  Purchase #4 $237.59   12.155%   $266.4691   $266.47   $266.45   $266.50  
  Purchase #5 $210.86   6.596%   $224.7683   $224.77   $224.75   $224.80  
  Purchase #6 $59.75   6.688%   $63.7461   $63.75   $63.75   $63.70  
  Purchase #7 $54.66   9.817%   $60.026   $60.03   $60.05   $60.00  
  7 purchase totals = $988.75       $1,087.3929   $1,087.40   $1,087.35   $1,087.50