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 $133.53   12.502%   $150.2239   $150.22   $150.20   $150.20  
  Purchase #2 $137.52   12.821%   $155.1514   $155.15   $155.15   $155.20  
  Purchase #3 $162.30   11.744%   $181.3605   $181.36   $181.35   $181.40  
  Purchase #4 $81.87   11.318%   $91.136   $91.14   $91.15   $91.10  
  Purchase #5 $18.54   11.264%   $20.6283   $20.63   $20.65   $20.60  
  Purchase #6 $7.97   3.645%   $8.2605   $8.26   $8.25   $8.30  
  Purchase #7 $216.42   8.522%   $234.8633   $234.86   $234.85   $234.90  
  7 purchase totals = $758.15       $841.6239   $841.62   $841.60   $841.70