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 $88.98   5.522%   $93.8935   $93.89   $93.90   $93.90  
  Purchase #2 $180.74   13.737%   $205.5683   $205.57   $205.55   $205.60  
  Purchase #3 $168.61   11.253%   $187.5837   $187.58   $187.60   $187.60  
  Purchase #4 $66.55   6.672%   $70.9902   $70.99   $71.00   $71.00  
  Purchase #5 $24.65   9.735%   $27.0497   $27.05   $27.05   $27.00  
  Purchase #6 $144.52   4.846%   $151.5234   $151.52   $151.50   $151.50  
  Purchase #7 $200.37   4.205%   $208.7956   $208.80   $208.80   $208.80  
  7 purchase totals = $874.42       $945.4044   $945.40   $945.40   $945.40