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 $236.36   4.363%   $246.6724   $246.67   $246.65   $246.70  
  Purchase #2 $188.65   3.751%   $195.7263   $195.73   $195.75   $195.70  
  Purchase #3 $165.70   6.343%   $176.2104   $176.21   $176.20   $176.20  
  Purchase #4 $12.79   5.864%   $13.54   $13.54   $13.55   $13.50  
  Purchase #5 $201.61   12.793%   $227.402   $227.40   $227.40   $227.40  
  Purchase #6 $163.28   9.507%   $178.803   $178.80   $178.80   $178.80  
  Purchase #7 $33.68   12.152%   $37.7728   $37.77   $37.75   $37.80  
  7 purchase totals = $1,002.07       $1,076.1269   $1,076.12   $1,076.10   $1,076.10