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 $53.52   11.780%   $59.8247   $59.82   $59.80   $59.80  
  Purchase #2 $145.94   8.786%   $158.7623   $158.76   $158.75   $158.80  
  Purchase #3 $185.61   10.292%   $204.713   $204.71   $204.70   $204.70  
  Purchase #4 $125.29   13.243%   $141.8822   $141.88   $141.90   $141.90  
  Purchase #5 $71.47   5.359%   $75.3001   $75.30   $75.30   $75.30  
  Purchase #6 $231.59   6.359%   $246.3168   $246.32   $246.30   $246.30  
  Purchase #7 $155.91   5.167%   $163.9659   $163.97   $163.95   $164.00  
  7 purchase totals = $969.33       $1,050.7650   $1,050.76   $1,050.70   $1,050.80