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 $113.77   9.516%   $124.5964   $124.60   $124.60   $124.60  
  Purchase #2 $82.53   12.533%   $92.8735   $92.87   $92.85   $92.90  
  Purchase #3 $207.61   4.516%   $216.9857   $216.99   $217.00   $217.00  
  Purchase #4 $71.75   7.590%   $77.1958   $77.20   $77.20   $77.20  
  Purchase #5 $69.42   6.502%   $73.9337   $73.93   $73.95   $73.90  
  Purchase #6 $209.60   9.716%   $229.9647   $229.96   $229.95   $230.00  
  Purchase #7 $166.63   7.815%   $179.6521   $179.65   $179.65   $179.70  
  7 purchase totals = $921.31       $995.2019   $995.20   $995.20   $995.30