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 $51.43   4.376%   $53.6806   $53.68   $53.70   $53.70  
  Purchase #2 $216.37   6.145%   $229.6659   $229.67   $229.65   $229.70  
  Purchase #3 $16.28   4.287%   $16.9779   $16.98   $17.00   $17.00  
  Purchase #4 $198.39   5.597%   $209.4939   $209.49   $209.50   $209.50  
  Purchase #5 $140.73   8.595%   $152.8257   $152.83   $152.85   $152.80  
  Purchase #6 $160.42   8.698%   $174.3733   $174.37   $174.35   $174.40  
  Purchase #7 $200.95   5.667%   $212.3378   $212.34   $212.35   $212.30  
  7 purchase totals = $984.57       $1,049.3551   $1,049.36   $1,049.40   $1,049.40