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 $24.43   4.598%   $25.5533   $25.55   $25.55   $25.60  
  Purchase #2 $127.87   4.806%   $134.0154   $134.02   $134.00   $134.00  
  Purchase #3 $68.70   7.544%   $73.8827   $73.88   $73.90   $73.90  
  Purchase #4 $163.59   12.798%   $184.5262   $184.53   $184.55   $184.50  
  Purchase #5 $203.52   10.240%   $224.3604   $224.36   $224.35   $224.40  
  Purchase #6 $213.56   4.389%   $222.9331   $222.93   $222.95   $222.90  
  Purchase #7 $151.59   10.776%   $167.9253   $167.93   $167.95   $167.90  
  7 purchase totals = $953.26       $1,033.1964   $1,033.20   $1,033.25   $1,033.20