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 $242.70   9.214%   $265.0624   $265.06   $265.05   $265.10  
  Purchase #2 $75.96   5.392%   $80.0558   $80.06   $80.05   $80.10  
  Purchase #3 $231.64   9.298%   $253.1779   $253.18   $253.20   $253.20  
  Purchase #4 $236.61   7.773%   $255.0017   $255.00   $255.00   $255.00  
  Purchase #5 $169.55   4.766%   $177.6308   $177.63   $177.65   $177.60  
  Purchase #6 $136.27   3.117%   $140.5175   $140.52   $140.50   $140.50  
  Purchase #7 $32.51   4.522%   $33.9801   $33.98   $34.00   $34.00  
  7 purchase totals = $1,125.24       $1,205.4262   $1,205.43   $1,205.45   $1,205.50