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 $210.61   6.558%   $224.4218   $224.42   $224.40   $224.40  
  Purchase #2 $15.80   6.107%   $16.7649   $16.76   $16.75   $16.80  
  Purchase #3 $139.75   4.608%   $146.1897   $146.19   $146.20   $146.20  
  Purchase #4 $173.68   11.415%   $193.5056   $193.51   $193.50   $193.50  
  Purchase #5 $106.57   11.654%   $118.9897   $118.99   $119.00   $119.00  
  Purchase #6 $121.31   3.627%   $125.7099   $125.71   $125.70   $125.70  
  Purchase #7 $219.37   7.678%   $236.2132   $236.21   $236.20   $236.20  
  7 purchase totals = $987.09       $1,061.7948   $1,061.79   $1,061.75   $1,061.80