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 $75.41   12.522%   $84.8528   $84.85   $84.85   $84.90  
  Purchase #2 $196.65   6.573%   $209.5758   $209.58   $209.60   $209.60  
  Purchase #3 $49.45   10.637%   $54.71   $54.71   $54.70   $54.70  
  Purchase #4 $226.79   5.730%   $239.7851   $239.79   $239.80   $239.80  
  Purchase #5 $115.25   7.659%   $124.077   $124.08   $124.10   $124.10  
  Purchase #6 $107.81   7.785%   $116.203   $116.20   $116.20   $116.20  
  Purchase #7 $174.35   11.655%   $194.6705   $194.67   $194.65   $194.70  
  7 purchase totals = $945.71       $1,023.8742   $1,023.88   $1,023.90   $1,024.00