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 $94.81   9.507%   $103.8236   $103.82   $103.80   $103.80  
  Purchase #2 $32.96   11.319%   $36.6907   $36.69   $36.70   $36.70  
  Purchase #3 $203.36   4.408%   $212.3241   $212.32   $212.30   $212.30  
  Purchase #4 $175.95   13.527%   $199.7508   $199.75   $199.75   $199.80  
  Purchase #5 $59.63   13.221%   $67.5137   $67.51   $67.50   $67.50  
  Purchase #6 $187.74   5.351%   $197.786   $197.79   $197.80   $197.80  
  Purchase #7 $232.91   6.776%   $248.692   $248.69   $248.70   $248.70  
  7 purchase totals = $987.36       $1,066.5809   $1,066.57   $1,066.55   $1,066.60