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 $227.34   12.663%   $256.1281   $256.13   $256.15   $256.10  
  Purchase #2 $133.88   11.566%   $149.3646   $149.36   $149.35   $149.40  
  Purchase #3 $191.32   6.103%   $202.9963   $203.00   $203.00   $203.00  
  Purchase #4 $69.95   7.234%   $75.0102   $75.01   $75.00   $75.00  
  Purchase #5 $116.44   10.380%   $128.5265   $128.53   $128.55   $128.50  
  Purchase #6 $56.56   10.639%   $62.5774   $62.58   $62.60   $62.60  
  Purchase #7 $218.86   12.481%   $246.1759   $246.18   $246.20   $246.20  
  7 purchase totals = $1,014.35       $1,120.7790   $1,120.79   $1,120.85   $1,120.80