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 $243.84   8.121%   $263.6422   $263.64   $263.65   $263.60  
  Purchase #2 $192.88   7.438%   $207.2264   $207.23   $207.25   $207.20  
  Purchase #3 $43.41   7.590%   $46.7048   $46.70   $46.70   $46.70  
  Purchase #4 $21.87   12.755%   $24.6595   $24.66   $24.65   $24.70  
  Purchase #5 $198.81   7.355%   $213.4325   $213.43   $213.45   $213.40  
  Purchase #6 $84.59   11.178%   $94.0455   $94.05   $94.05   $94.00  
  Purchase #7 $76.44   6.659%   $81.5301   $81.53   $81.55   $81.50  
  7 purchase totals = $861.84       $931.2410   $931.24   $931.30   $931.10