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 $191.54   6.494%   $203.9786   $203.98   $204.00   $204.00  
  Purchase #2 $26.54   13.251%   $30.0568   $30.06   $30.05   $30.10  
  Purchase #3 $57.46   3.281%   $59.3453   $59.35   $59.35   $59.30  
  Purchase #4 $235.71   4.532%   $246.3924   $246.39   $246.40   $246.40  
  Purchase #5 $6.39   8.640%   $6.9421   $6.94   $6.95   $6.90  
  Purchase #6 $32.54   4.189%   $33.9031   $33.90   $33.90   $33.90  
  Purchase #7 $114.77   9.532%   $125.7099   $125.71   $125.70   $125.70  
  7 purchase totals = $664.95       $706.3282   $706.33   $706.35   $706.30