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 $57.65   6.332%   $61.3004   $61.30   $61.30   $61.30  
  Purchase #2 $187.78   12.528%   $211.3051   $211.31   $211.30   $211.30  
  Purchase #3 $246.52   9.622%   $270.2402   $270.24   $270.25   $270.20  
  Purchase #4 $162.31   10.272%   $178.9825   $178.98   $179.00   $179.00  
  Purchase #5 $8.34   6.262%   $8.8623   $8.86   $8.85   $8.90  
  Purchase #6 $80.38   13.820%   $91.4885   $91.49   $91.50   $91.50  
  Purchase #7 $125.65   8.516%   $136.3504   $136.35   $136.35   $136.40  
  7 purchase totals = $868.63       $958.5294   $958.53   $958.55   $958.60