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 $125.83   12.229%   $141.2178   $141.22   $141.20   $141.20  
  Purchase #2 $94.51   8.194%   $102.2541   $102.25   $102.25   $102.30  
  Purchase #3 $119.28   11.179%   $132.6143   $132.61   $132.60   $132.60  
  Purchase #4 $50.60   8.586%   $54.9445   $54.94   $54.95   $54.90  
  Purchase #5 $135.77   5.871%   $143.7411   $143.74   $143.75   $143.70  
  Purchase #6 $244.40   9.220%   $266.9337   $266.93   $266.95   $266.90  
  Purchase #7 $228.85   10.439%   $252.7397   $252.74   $252.75   $252.70  
  7 purchase totals = $999.24       $1,094.4452   $1,094.43   $1,094.45   $1,094.30