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 $58.29   13.606%   $66.2209   $66.22   $66.20   $66.20  
  Purchase #2 $189.64   11.137%   $210.7602   $210.76   $210.75   $210.80  
  Purchase #3 $89.41   12.652%   $100.7222   $100.72   $100.70   $100.70  
  Purchase #4 $221.86   9.617%   $243.1963   $243.20   $243.20   $243.20  
  Purchase #5 $227.93   11.678%   $254.5477   $254.55   $254.55   $254.50  
  Purchase #6 $149.77   7.862%   $161.5449   $161.54   $161.55   $161.50  
  Purchase #7 $35.33   12.839%   $39.866   $39.87   $39.85   $39.90  
  7 purchase totals = $972.23       $1,076.8582   $1,076.86   $1,076.80   $1,076.80