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 $65.54   6.714%   $69.9404   $69.94   $69.95   $69.90  
  Purchase #2 $239.67   11.369%   $266.9181   $266.92   $266.90   $266.90  
  Purchase #3 $197.84   12.412%   $222.3959   $222.40   $222.40   $222.40  
  Purchase #4 $52.40   12.352%   $58.8724   $58.87   $58.85   $58.90  
  Purchase #5 $97.31   11.384%   $108.3878   $108.39   $108.40   $108.40  
  Purchase #6 $125.62   7.211%   $134.6785   $134.68   $134.70   $134.70  
  Purchase #7 $94.98   9.722%   $104.214   $104.21   $104.20   $104.20  
  7 purchase totals = $873.36       $965.4071   $965.41   $965.40   $965.40