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 $173.93   11.823%   $194.4937   $194.49   $194.50   $194.50  
  Purchase #2 $62.49   5.566%   $65.9682   $65.97   $65.95   $66.00  
  Purchase #3 $217.37   5.161%   $228.5885   $228.59   $228.60   $228.60  
  Purchase #4 $198.46   6.819%   $211.993   $211.99   $212.00   $212.00  
  Purchase #5 $72.74   8.746%   $79.1018   $79.10   $79.10   $79.10  
  Purchase #6 $40.56   12.353%   $45.5704   $45.57   $45.55   $45.60  
  Purchase #7 $70.85   8.658%   $76.9842   $76.98   $77.00   $77.00  
  7 purchase totals = $836.40       $902.6998   $902.69   $902.70   $902.80