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 $61.81   7.399%   $66.3833   $66.38   $66.40   $66.40  
  Purchase #2 $165.54   12.531%   $186.2838   $186.28   $186.30   $186.30  
  Purchase #3 $10.94   5.817%   $11.5764   $11.58   $11.60   $11.60  
  Purchase #4 $161.43   12.437%   $181.507   $181.51   $181.50   $181.50  
  Purchase #5 $137.61   9.214%   $150.2894   $150.29   $150.30   $150.30  
  Purchase #6 $175.79   10.249%   $193.8067   $193.81   $193.80   $193.80  
  Purchase #7 $154.37   8.666%   $167.7477   $167.75   $167.75   $167.70  
  7 purchase totals = $867.49       $957.5943   $957.60   $957.65   $957.60