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 $55.47   12.776%   $62.5568   $62.56   $62.55   $62.60  
  Purchase #2 $213.36   11.687%   $238.2954   $238.30   $238.30   $238.30  
  Purchase #3 $39.60   3.607%   $41.0284   $41.03   $41.05   $41.00  
  Purchase #4 $103.31   9.429%   $113.0511   $113.05   $113.05   $113.10  
  Purchase #5 $219.71   5.265%   $231.2777   $231.28   $231.30   $231.30  
  Purchase #6 $91.63   5.809%   $96.9528   $96.95   $96.95   $97.00  
  Purchase #7 $234.59   7.440%   $252.0435   $252.04   $252.05   $252.00  
  7 purchase totals = $957.67       $1,035.2057   $1,035.21   $1,035.25   $1,035.30