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 $43.39   7.812%   $46.7796   $46.78   $46.80   $46.80  
  Purchase #2 $229.65   6.192%   $243.8699   $243.87   $243.85   $243.90  
  Purchase #3 $249.28   11.636%   $278.2862   $278.29   $278.30   $278.30  
  Purchase #4 $12.56   12.779%   $14.165   $14.17   $14.15   $14.20  
  Purchase #5 $136.94   13.155%   $154.9545   $154.95   $154.95   $155.00  
  Purchase #6 $65.36   9.808%   $71.7705   $71.77   $71.75   $71.80  
  Purchase #7 $223.88   7.269%   $240.1538   $240.15   $240.15   $240.20  
  7 purchase totals = $961.06       $1,049.9795   $1,049.98   $1,049.95   $1,050.20