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 $66.80   11.551%   $74.5161   $74.52   $74.50   $74.50  
  Purchase #2 $61.85   3.485%   $64.0055   $64.01   $64.00   $64.00  
  Purchase #3 $56.39   7.582%   $60.6655   $60.67   $60.65   $60.70  
  Purchase #4 $246.69   11.463%   $274.9681   $274.97   $274.95   $275.00  
  Purchase #5 $163.25   4.730%   $170.9717   $170.97   $170.95   $171.00  
  Purchase #6 $162.78   12.383%   $182.937   $182.94   $182.95   $182.90  
  Purchase #7 $30.84   7.155%   $33.0466   $33.05   $33.05   $33.00  
  7 purchase totals = $788.60       $861.1105   $861.13   $861.05   $861.10