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 $61.87   10.824%   $68.5668   $68.57   $68.55   $68.60  
  Purchase #2 $145.75   12.853%   $164.4832   $164.48   $164.50   $164.50  
  Purchase #3 $73.67   12.343%   $82.7631   $82.76   $82.75   $82.80  
  Purchase #4 $172.73   6.244%   $183.5153   $183.52   $183.50   $183.50  
  Purchase #5 $110.75   13.573%   $125.7821   $125.78   $125.80   $125.80  
  Purchase #6 $201.37   8.157%   $217.7958   $217.80   $217.80   $217.80  
  Purchase #7 $41.46   10.707%   $45.8991   $45.90   $45.90   $45.90  
  7 purchase totals = $807.60       $888.8054   $888.81   $888.80   $888.90