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 $88.47   4.434%   $92.3928   $92.39   $92.40   $92.40  
  Purchase #2 $170.91   7.107%   $183.0566   $183.06   $183.05   $183.10  
  Purchase #3 $232.84   8.584%   $252.827   $252.83   $252.85   $252.80  
  Purchase #4 $165.76   5.579%   $175.0078   $175.01   $175.00   $175.00  
  Purchase #5 $131.94   11.121%   $146.613   $146.61   $146.60   $146.60  
  Purchase #6 $84.30   6.233%   $89.5544   $89.55   $89.55   $89.60  
  Purchase #7 $12.38   10.408%   $13.6685   $13.67   $13.65   $13.70  
  7 purchase totals = $886.60       $953.1201   $953.12   $953.10   $953.20