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 $220.52   11.547%   $245.9834   $245.98   $246.00   $246.00  
  Purchase #2 $233.33   7.267%   $250.2861   $250.29   $250.30   $250.30  
  Purchase #3 $161.72   9.319%   $176.7907   $176.79   $176.80   $176.80  
  Purchase #4 $233.67   10.199%   $257.502   $257.50   $257.50   $257.50  
  Purchase #5 $202.40   11.535%   $225.7468   $225.75   $225.75   $225.70  
  Purchase #6 $202.93   6.828%   $216.7861   $216.79   $216.80   $216.80  
  Purchase #7 $99.37   11.427%   $110.725   $110.73   $110.75   $110.70  
  7 purchase totals = $1,353.94       $1,483.8201   $1,483.83   $1,483.90   $1,483.80