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 $242.59   7.217%   $260.0977   $260.10   $260.10   $260.10  
  Purchase #2 $203.78   13.251%   $230.7829   $230.78   $230.80   $230.80  
  Purchase #3 $65.68   12.852%   $74.1212   $74.12   $74.10   $74.10  
  Purchase #4 $151.65   3.820%   $157.443   $157.44   $157.45   $157.40  
  Purchase #5 $90.50   7.684%   $97.454   $97.45   $97.45   $97.50  
  Purchase #6 $43.49   3.628%   $45.0678   $45.07   $45.05   $45.10  
  Purchase #7 $235.91   9.592%   $258.5385   $258.54   $258.55   $258.50  
  7 purchase totals = $1,033.60       $1,123.5051   $1,123.50   $1,123.50   $1,123.50