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 $184.37   10.811%   $204.3022   $204.30   $204.30   $204.30  
  Purchase #2 $105.80   11.470%   $117.9353   $117.94   $117.95   $117.90  
  Purchase #3 $19.56   8.197%   $21.1633   $21.16   $21.15   $21.20  
  Purchase #4 $215.57   4.736%   $225.7794   $225.78   $225.80   $225.80  
  Purchase #5 $194.35   11.487%   $216.675   $216.68   $216.70   $216.70  
  Purchase #6 $56.70   5.301%   $59.7057   $59.71   $59.70   $59.70  
  Purchase #7 $145.90   13.806%   $166.043   $166.04   $166.05   $166.00  
  7 purchase totals = $922.25       $1,011.6039   $1,011.61   $1,011.65   $1,011.60