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 $203.53   6.383%   $216.5213   $216.52   $216.50   $216.50  
  Purchase #2 $169.43   3.260%   $174.9534   $174.95   $174.95   $175.00  
  Purchase #3 $165.29   13.169%   $187.057   $187.06   $187.05   $187.10  
  Purchase #4 $176.76   11.816%   $197.646   $197.65   $197.65   $197.60  
  Purchase #5 $210.63   13.117%   $238.2583   $238.26   $238.25   $238.30  
  Purchase #6 $219.40   10.479%   $242.3909   $242.39   $242.40   $242.40  
  Purchase #7 $154.57   4.276%   $161.1794   $161.18   $161.20   $161.20  
  7 purchase totals = $1,299.61       $1,418.0063   $1,418.01   $1,418.00   $1,418.10