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 $107.84   10.550%   $119.2171   $119.22   $119.20   $119.20  
  Purchase #2 $174.87   8.829%   $190.3093   $190.31   $190.30   $190.30  
  Purchase #3 $7.26   5.112%   $7.6311   $7.63   $7.65   $7.60  
  Purchase #4 $241.34   6.281%   $256.4986   $256.50   $256.50   $256.50  
  Purchase #5 $131.99   5.828%   $139.6824   $139.68   $139.70   $139.70  
  Purchase #6 $96.71   4.222%   $100.7931   $100.79   $100.80   $100.80  
  Purchase #7 $164.48   9.663%   $180.3737   $180.37   $180.35   $180.40  
  7 purchase totals = $924.49       $994.5053   $994.50   $994.50   $994.50