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 $24.59   3.787%   $25.5212   $25.52   $25.50   $25.50  
  Purchase #2 $172.53   3.586%   $178.7169   $178.72   $178.70   $178.70  
  Purchase #3 $108.72   3.449%   $112.4698   $112.47   $112.45   $112.50  
  Purchase #4 $113.37   7.506%   $121.8796   $121.88   $121.90   $121.90  
  Purchase #5 $166.46   3.789%   $172.7672   $172.77   $172.75   $172.80  
  Purchase #6 $168.45   3.480%   $174.3121   $174.31   $174.30   $174.30  
  Purchase #7 $127.37   10.449%   $140.6789   $140.68   $140.70   $140.70  
  7 purchase totals = $881.49       $926.3457   $926.35   $926.30   $926.40