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 $63.81   5.492%   $67.3144   $67.31   $67.30   $67.30  
  Purchase #2 $163.58   7.808%   $176.3523   $176.35   $176.35   $176.40  
  Purchase #3 $242.83   7.456%   $260.9354   $260.94   $260.95   $260.90  
  Purchase #4 $47.66   10.277%   $52.558   $52.56   $52.55   $52.60  
  Purchase #5 $83.99   5.120%   $88.2903   $88.29   $88.30   $88.30  
  Purchase #6 $198.39   5.852%   $209.9998   $210.00   $210.00   $210.00  
  Purchase #7 $168.87   13.733%   $192.0609   $192.06   $192.05   $192.10  
  7 purchase totals = $969.13       $1,047.5111   $1,047.51   $1,047.50   $1,047.60