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 $96.59   12.314%   $108.4841   $108.48   $108.50   $108.50  
  Purchase #2 $120.36   9.614%   $131.9314   $131.93   $131.95   $131.90  
  Purchase #3 $159.25   10.872%   $176.5637   $176.56   $176.55   $176.60  
  Purchase #4 $126.30   7.696%   $136.02   $136.02   $136.00   $136.00  
  Purchase #5 $171.48   13.831%   $195.1974   $195.20   $195.20   $195.20  
  Purchase #6 $64.85   11.362%   $72.2183   $72.22   $72.20   $72.20  
  Purchase #7 $156.50   12.107%   $175.4475   $175.45   $175.45   $175.40  
  7 purchase totals = $895.33       $995.8624   $995.86   $995.85   $995.80