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 $88.80   8.796%   $96.6108   $96.61   $96.60   $96.60  
  Purchase #2 $24.32   5.692%   $25.7043   $25.70   $25.70   $25.70  
  Purchase #3 $154.78   6.313%   $164.5513   $164.55   $164.55   $164.60  
  Purchase #4 $230.62   6.477%   $245.5573   $245.56   $245.55   $245.60  
  Purchase #5 $22.86   6.672%   $24.3852   $24.39   $24.40   $24.40  
  Purchase #6 $44.90   10.561%   $49.6419   $49.64   $49.65   $49.60  
  Purchase #7 $203.43   13.775%   $231.4525   $231.45   $231.45   $231.50  
  7 purchase totals = $769.71       $837.9033   $837.90   $837.90   $838.00