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 $216.85   7.303%   $232.6866   $232.69   $232.70   $232.70  
  Purchase #2 $69.37   7.618%   $74.6546   $74.65   $74.65   $74.70  
  Purchase #3 $52.57   10.608%   $58.1466   $58.15   $58.15   $58.10  
  Purchase #4 $88.82   4.850%   $93.1278   $93.13   $93.15   $93.10  
  Purchase #5 $208.46   10.310%   $229.9522   $229.95   $229.95   $230.00  
  Purchase #6 $33.93   4.183%   $35.3493   $35.35   $35.35   $35.30  
  Purchase #7 $91.85   7.657%   $98.883   $98.88   $98.90   $98.90  
  7 purchase totals = $761.85       $822.8001   $822.80   $822.85   $822.80