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 $66.99   12.761%   $75.5386   $75.54   $75.55   $75.50  
  Purchase #2 $225.57   11.120%   $250.6534   $250.65   $250.65   $250.70  
  Purchase #3 $7.95   10.371%   $8.7745   $8.77   $8.75   $8.80  
  Purchase #4 $147.90   3.472%   $153.0351   $153.04   $153.05   $153.00  
  Purchase #5 $161.74   3.166%   $166.8607   $166.86   $166.85   $166.90  
  Purchase #6 $14.94   9.351%   $16.337   $16.34   $16.35   $16.30  
  Purchase #7 $33.47   10.476%   $36.9763   $36.98   $37.00   $37.00  
  7 purchase totals = $658.56       $708.1756   $708.18   $708.20   $708.20