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 $245.49   10.396%   $271.0111   $271.01   $271.00   $271.00  
  Purchase #2 $135.62   11.341%   $151.0007   $151.00   $151.00   $151.00  
  Purchase #3 $205.75   12.144%   $230.7363   $230.74   $230.75   $230.70  
  Purchase #4 $67.63   5.388%   $71.2739   $71.27   $71.25   $71.30  
  Purchase #5 $57.43   6.102%   $60.9344   $60.93   $60.95   $60.90  
  Purchase #6 $107.60   10.115%   $118.4837   $118.48   $118.50   $118.50  
  Purchase #7 $128.78   7.320%   $138.2067   $138.21   $138.20   $138.20  
  7 purchase totals = $948.30       $1,041.6468   $1,041.64   $1,041.65   $1,041.60