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 $83.84   10.558%   $92.6918   $92.69   $92.70   $92.70  
  Purchase #2 $170.99   4.397%   $178.5084   $178.51   $178.50   $178.50  
  Purchase #3 $181.46   12.618%   $204.3566   $204.36   $204.35   $204.40  
  Purchase #4 $67.51   4.574%   $70.5979   $70.60   $70.60   $70.60  
  Purchase #5 $125.70   9.680%   $137.8678   $137.87   $137.85   $137.90  
  Purchase #6 $206.25   8.757%   $224.3113   $224.31   $224.30   $224.30  
  Purchase #7 $41.62   8.234%   $45.047   $45.05   $45.05   $45.00  
  7 purchase totals = $877.37       $953.3808   $953.39   $953.35   $953.40