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 $67.55   13.291%   $76.5281   $76.53   $76.55   $76.50  
  Purchase #2 $215.87   12.287%   $242.3939   $242.39   $242.40   $242.40  
  Purchase #3 $136.72   3.556%   $141.5818   $141.58   $141.60   $141.60  
  Purchase #4 $210.50   10.212%   $231.9963   $232.00   $232.00   $232.00  
  Purchase #5 $156.34   6.195%   $166.0253   $166.03   $166.05   $166.00  
  Purchase #6 $43.51   4.820%   $45.6072   $45.61   $45.60   $45.60  
  Purchase #7 $7.31   4.654%   $7.6502   $7.65   $7.65   $7.70  
  7 purchase totals = $837.80       $911.7828   $911.79   $911.85   $911.80