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 $53.36   11.189%   $59.3305   $59.33   $59.35   $59.30  
  Purchase #2 $67.50   10.511%   $74.5949   $74.59   $74.60   $74.60  
  Purchase #3 $196.57   10.227%   $216.6732   $216.67   $216.65   $216.70  
  Purchase #4 $157.35   11.766%   $175.8638   $175.86   $175.85   $175.90  
  Purchase #5 $9.26   4.433%   $9.6705   $9.67   $9.65   $9.70  
  Purchase #6 $190.86   7.869%   $205.8788   $205.88   $205.90   $205.90  
  Purchase #7 $141.99   8.300%   $153.7752   $153.78   $153.80   $153.80  
  7 purchase totals = $816.89       $895.7869   $895.78   $895.80   $895.90