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 $125.69   5.276%   $132.3214   $132.32   $132.30   $132.30  
  Purchase #2 $213.25   5.188%   $224.3134   $224.31   $224.30   $224.30  
  Purchase #3 $134.98   11.358%   $150.311   $150.31   $150.30   $150.30  
  Purchase #4 $88.82   8.211%   $96.113   $96.11   $96.10   $96.10  
  Purchase #5 $48.45   12.788%   $54.6458   $54.65   $54.65   $54.60  
  Purchase #6 $204.63   3.318%   $211.4196   $211.42   $211.40   $211.40  
  Purchase #7 $163.89   10.423%   $180.9723   $180.97   $180.95   $181.00  
  7 purchase totals = $979.71       $1,050.0965   $1,050.09   $1,050.00   $1,050.00