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 $70.90   4.300%   $73.9487   $73.95   $73.95   $73.90  
  Purchase #2 $146.32   9.309%   $159.9409   $159.94   $159.95   $159.90  
  Purchase #3 $198.52   13.829%   $225.9733   $225.97   $225.95   $226.00  
  Purchase #4 $208.84   13.133%   $236.267   $236.27   $236.25   $236.30  
  Purchase #5 $90.83   5.858%   $96.1508   $96.15   $96.15   $96.20  
  Purchase #6 $48.25   5.372%   $50.842   $50.84   $50.85   $50.80  
  Purchase #7 $210.53   13.147%   $238.2084   $238.21   $238.20   $238.20  
  7 purchase totals = $974.19       $1,081.3311   $1,081.33   $1,081.30   $1,081.30