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 $47.69   8.171%   $51.5867   $51.59   $51.60   $51.60  
  Purchase #2 $117.61   6.470%   $125.2194   $125.22   $125.20   $125.20  
  Purchase #3 $37.25   13.786%   $42.3853   $42.39   $42.40   $42.40  
  Purchase #4 $110.49   12.851%   $124.6891   $124.69   $124.70   $124.70  
  Purchase #5 $238.59   9.818%   $262.0148   $262.01   $262.00   $262.00  
  Purchase #6 $205.61   7.345%   $220.7121   $220.71   $220.70   $220.70  
  Purchase #7 $150.42   13.165%   $170.2228   $170.22   $170.20   $170.20  
  7 purchase totals = $907.66       $996.8302   $996.83   $996.80   $996.80