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 $210.61   6.761%   $224.8493   $224.85   $224.85   $224.80  
  Purchase #2 $184.49   8.514%   $200.1975   $200.20   $200.20   $200.20  
  Purchase #3 $226.39   6.810%   $241.8072   $241.81   $241.80   $241.80  
  Purchase #4 $100.67   3.855%   $104.5508   $104.55   $104.55   $104.60  
  Purchase #5 $7.92   5.623%   $8.3653   $8.37   $8.35   $8.40  
  Purchase #6 $48.49   12.337%   $54.4722   $54.47   $54.45   $54.50  
  Purchase #7 $162.31   13.390%   $184.0433   $184.04   $184.05   $184.00  
  7 purchase totals = $940.88       $1,018.2856   $1,018.29   $1,018.25   $1,018.30