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 $70.79   7.812%   $76.3201   $76.32   $76.30   $76.30  
  Purchase #2 $198.35   4.517%   $207.3095   $207.31   $207.30   $207.30  
  Purchase #3 $226.93   4.724%   $237.6502   $237.65   $237.65   $237.70  
  Purchase #4 $110.49   13.119%   $124.9852   $124.99   $125.00   $125.00  
  Purchase #5 $172.90   13.319%   $195.9286   $195.93   $195.95   $195.90  
  Purchase #6 $64.95   8.623%   $70.5506   $70.55   $70.55   $70.60  
  Purchase #7 $109.63   10.804%   $121.4744   $121.47   $121.45   $121.50  
  7 purchase totals = $954.04       $1,034.2186   $1,034.22   $1,034.20   $1,034.30