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 $32.56   5.471%   $34.3414   $34.34   $34.35   $34.30  
  Purchase #2 $61.57   8.127%   $66.5738   $66.57   $66.55   $66.60  
  Purchase #3 $212.46   11.486%   $236.8632   $236.86   $236.85   $236.90  
  Purchase #4 $48.41   3.765%   $50.2326   $50.23   $50.25   $50.20  
  Purchase #5 $77.97   9.472%   $85.3553   $85.36   $85.35   $85.40  
  Purchase #6 $81.42   8.465%   $88.3122   $88.31   $88.30   $88.30  
  Purchase #7 $221.68   3.599%   $229.6583   $229.66   $229.65   $229.70  
  7 purchase totals = $736.07       $791.3368   $791.33   $791.30   $791.40