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 $226.39   13.528%   $257.016   $257.02   $257.00   $257.00  
  Purchase #2 $109.66   3.688%   $113.7043   $113.70   $113.70   $113.70  
  Purchase #3 $199.43   10.443%   $220.2565   $220.26   $220.25   $220.30  
  Purchase #4 $242.94   10.394%   $268.1912   $268.19   $268.20   $268.20  
  Purchase #5 $202.93   5.813%   $214.7263   $214.73   $214.75   $214.70  
  Purchase #6 $203.96   7.832%   $219.9341   $219.93   $219.95   $219.90  
  Purchase #7 $77.78   12.328%   $87.3687   $87.37   $87.35   $87.40  
  7 purchase totals = $1,263.09       $1,381.1971   $1,381.20   $1,381.20   $1,381.20