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 $55.57   6.256%   $59.0465   $59.05   $59.05   $59.00  
  Purchase #2 $107.74   13.791%   $122.5984   $122.60   $122.60   $122.60  
  Purchase #3 $16.31   4.647%   $17.0679   $17.07   $17.05   $17.10  
  Purchase #4 $96.56   3.214%   $99.6634   $99.66   $99.65   $99.70  
  Purchase #5 $55.85   9.485%   $61.1474   $61.15   $61.15   $61.10  
  Purchase #6 $234.26   9.482%   $256.4725   $256.47   $256.45   $256.50  
  Purchase #7 $48.99   12.490%   $55.1089   $55.11   $55.10   $55.10  
  7 purchase totals = $615.28       $671.1050   $671.11   $671.05   $671.10