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 $89.92   4.377%   $93.8558   $93.86   $93.85   $93.90  
  Purchase #2 $188.66   5.643%   $199.3061   $199.31   $199.30   $199.30  
  Purchase #3 $226.72   3.796%   $235.3263   $235.33   $235.35   $235.30  
  Purchase #4 $96.43   12.786%   $108.7595   $108.76   $108.75   $108.80  
  Purchase #5 $224.96   7.792%   $242.4889   $242.49   $242.50   $242.50  
  Purchase #6 $58.92   6.280%   $62.6202   $62.62   $62.60   $62.60  
  Purchase #7 $22.45   8.231%   $24.2979   $24.30   $24.30   $24.30  
  7 purchase totals = $908.06       $966.6547   $966.67   $966.65   $966.70