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 $185.69   8.670%   $201.7893   $201.79   $201.80   $201.80  
  Purchase #2 $162.27   5.175%   $170.6675   $170.67   $170.65   $170.70  
  Purchase #3 $181.74   4.176%   $189.3295   $189.33   $189.35   $189.30  
  Purchase #4 $197.34   3.624%   $204.4916   $204.49   $204.50   $204.50  
  Purchase #5 $93.88   11.409%   $104.5908   $104.59   $104.60   $104.60  
  Purchase #6 $137.41   6.190%   $145.9157   $145.92   $145.90   $145.90  
  Purchase #7 $8.43   4.514%   $8.8105   $8.81   $8.80   $8.80  
  7 purchase totals = $966.76       $1,025.5949   $1,025.60   $1,025.60   $1,025.60