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 $46.61   4.174%   $48.5555   $48.56   $48.55   $48.60  
  Purchase #2 $143.95   4.772%   $150.8193   $150.82   $150.80   $150.80  
  Purchase #3 $229.96   3.551%   $238.1259   $238.13   $238.15   $238.10  
  Purchase #4 $128.64   4.216%   $134.0635   $134.06   $134.05   $134.10  
  Purchase #5 $56.46   10.252%   $62.2483   $62.25   $62.25   $62.20  
  Purchase #6 $123.50   6.706%   $131.7819   $131.78   $131.80   $131.80  
  Purchase #7 $220.58   6.629%   $235.2022   $235.20   $235.20   $235.20  
  7 purchase totals = $949.70       $1,000.7966   $1,000.80   $1,000.80   $1,000.80