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 $56.52   7.506%   $60.7624   $60.76   $60.75   $60.80  
  Purchase #2 $147.78   11.198%   $164.3284   $164.33   $164.35   $164.30  
  Purchase #3 $127.54   10.221%   $140.5759   $140.58   $140.60   $140.60  
  Purchase #4 $182.69   7.170%   $195.7889   $195.79   $195.80   $195.80  
  Purchase #5 $128.94   13.708%   $146.6151   $146.62   $146.60   $146.60  
  Purchase #6 $13.92   3.626%   $14.4247   $14.42   $14.40   $14.40  
  Purchase #7 $161.44   9.114%   $176.1536   $176.15   $176.15   $176.20  
  7 purchase totals = $818.83       $898.6490   $898.65   $898.65   $898.70