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 $226.49   4.171%   $235.9369   $235.94   $235.95   $235.90  
  Purchase #2 $241.42   9.516%   $264.3935   $264.39   $264.40   $264.40  
  Purchase #3 $33.58   5.770%   $35.5176   $35.52   $35.50   $35.50  
  Purchase #4 $110.86   9.681%   $121.5924   $121.59   $121.60   $121.60  
  Purchase #5 $173.68   12.259%   $194.9714   $194.97   $194.95   $195.00  
  Purchase #6 $174.77   7.769%   $188.3479   $188.35   $188.35   $188.30  
  Purchase #7 $57.84   4.200%   $60.2693   $60.27   $60.25   $60.30  
  7 purchase totals = $1,018.64       $1,101.0290   $1,101.03   $1,101.00   $1,101.00