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 $188.89   6.858%   $201.8441   $201.84   $201.85   $201.80  
  Purchase #2 $225.95   12.477%   $254.1418   $254.14   $254.15   $254.10  
  Purchase #3 $220.32   6.152%   $233.8741   $233.87   $233.85   $233.90  
  Purchase #4 $93.35   12.484%   $105.0038   $105.00   $105.00   $105.00  
  Purchase #5 $15.93   9.591%   $17.4578   $17.46   $17.45   $17.50  
  Purchase #6 $182.48   6.690%   $194.6879   $194.69   $194.70   $194.70  
  Purchase #7 $59.35   12.620%   $66.84   $66.84   $66.85   $66.80  
  7 purchase totals = $986.27       $1,073.8495   $1,073.84   $1,073.85   $1,073.80