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 $191.60   13.201%   $216.8931   $216.89   $216.90   $216.90  
  Purchase #2 $134.62   4.474%   $140.6429   $140.64   $140.65   $140.60  
  Purchase #3 $5.85   12.113%   $6.5586   $6.56   $6.55   $6.60  
  Purchase #4 $64.96   9.824%   $71.3417   $71.34   $71.35   $71.30  
  Purchase #5 $140.97   3.405%   $145.77   $145.77   $145.75   $145.80  
  Purchase #6 $86.94   8.727%   $94.5273   $94.53   $94.55   $94.50  
  Purchase #7 $61.30   7.671%   $66.0023   $66.00   $66.00   $66.00  
  7 purchase totals = $686.24       $741.7359   $741.73   $741.75   $741.70