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 $195.93   3.582%   $202.9482   $202.95   $202.95   $202.90  
  Purchase #2 $88.95   8.523%   $96.5312   $96.53   $96.55   $96.50  
  Purchase #3 $141.40   12.841%   $159.5572   $159.56   $159.55   $159.60  
  Purchase #4 $83.34   6.468%   $88.7304   $88.73   $88.75   $88.70  
  Purchase #5 $177.69   3.549%   $183.9962   $184.00   $184.00   $184.00  
  Purchase #6 $85.94   11.296%   $95.6478   $95.65   $95.65   $95.60  
  Purchase #7 $39.93   5.558%   $42.1493   $42.15   $42.15   $42.10  
  7 purchase totals = $813.18       $869.5603   $869.57   $869.60   $869.40