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 $116.88   11.519%   $130.3434   $130.34   $130.35   $130.30  
  Purchase #2 $60.82   9.426%   $66.5529   $66.55   $66.55   $66.60  
  Purchase #3 $132.83   11.605%   $148.2449   $148.24   $148.25   $148.20  
  Purchase #4 $214.67   4.758%   $224.884   $224.88   $224.90   $224.90  
  Purchase #5 $80.55   5.264%   $84.7902   $84.79   $84.80   $84.80  
  Purchase #6 $185.64   8.300%   $201.0481   $201.05   $201.05   $201.00  
  Purchase #7 $179.31   3.343%   $185.3043   $185.30   $185.30   $185.30  
  7 purchase totals = $970.70       $1,041.1678   $1,041.15   $1,041.20   $1,041.10