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 $211.93   6.569%   $225.8517   $225.85   $225.85   $225.90  
  Purchase #2 $146.58   13.775%   $166.7714   $166.77   $166.75   $166.80  
  Purchase #3 $172.27   6.163%   $182.887   $182.89   $182.90   $182.90  
  Purchase #4 $80.59   9.651%   $88.3677   $88.37   $88.35   $88.40  
  Purchase #5 $35.80   11.445%   $39.8973   $39.90   $39.90   $39.90  
  Purchase #6 $221.29   4.437%   $231.1086   $231.11   $231.10   $231.10  
  Purchase #7 $57.65   4.421%   $60.1987   $60.20   $60.20   $60.20  
  7 purchase totals = $926.11       $995.0824   $995.09   $995.05   $995.20