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 $22.67   13.468%   $25.7232   $25.72   $25.70   $25.70  
  Purchase #2 $73.94   7.146%   $79.2238   $79.22   $79.20   $79.20  
  Purchase #3 $64.61   13.576%   $73.3815   $73.38   $73.40   $73.40  
  Purchase #4 $238.65   10.184%   $262.9541   $262.95   $262.95   $263.00  
  Purchase #5 $141.27   11.562%   $157.6036   $157.60   $157.60   $157.60  
  Purchase #6 $239.79   11.685%   $267.8095   $267.81   $267.80   $267.80  
  Purchase #7 $184.98   8.192%   $200.1336   $200.13   $200.15   $200.10  
  7 purchase totals = $965.91       $1,066.8293   $1,066.81   $1,066.80   $1,066.80