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 $216.79   7.573%   $233.2075   $233.21   $233.20   $233.20  
  Purchase #2 $137.79   8.104%   $148.9565   $148.96   $148.95   $149.00  
  Purchase #3 $82.41   7.281%   $88.4103   $88.41   $88.40   $88.40  
  Purchase #4 $138.28   8.404%   $149.9011   $149.90   $149.90   $149.90  
  Purchase #5 $83.50   7.151%   $89.4711   $89.47   $89.45   $89.50  
  Purchase #6 $236.26   7.660%   $254.3575   $254.36   $254.35   $254.40  
  Purchase #7 $97.53   13.618%   $110.8116   $110.81   $110.80   $110.80  
  7 purchase totals = $992.56       $1,075.1156   $1,075.12   $1,075.05   $1,075.20