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 $46.81   12.504%   $52.6631   $52.66   $52.65   $52.70  
  Purchase #2 $204.87   9.485%   $224.3019   $224.30   $224.30   $224.30  
  Purchase #3 $102.38   13.535%   $116.2371   $116.24   $116.25   $116.20  
  Purchase #4 $176.62   10.398%   $194.9849   $194.98   $195.00   $195.00  
  Purchase #5 $120.97   10.762%   $133.9888   $133.99   $134.00   $134.00  
  Purchase #6 $93.47   13.134%   $105.7463   $105.75   $105.75   $105.70  
  Purchase #7 $172.57   11.495%   $192.4069   $192.41   $192.40   $192.40  
  7 purchase totals = $917.69       $1,020.3290   $1,020.33   $1,020.35   $1,020.30