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 $217.33   12.571%   $244.6506   $244.65   $244.65   $244.70  
  Purchase #2 $26.58   4.407%   $27.7514   $27.75   $27.75   $27.80  
  Purchase #3 $152.58   11.653%   $170.3601   $170.36   $170.35   $170.40  
  Purchase #4 $112.65   7.767%   $121.3995   $121.40   $121.40   $121.40  
  Purchase #5 $31.41   4.111%   $32.7013   $32.70   $32.70   $32.70  
  Purchase #6 $139.65   7.231%   $149.7481   $149.75   $149.75   $149.70  
  Purchase #7 $246.28   6.851%   $263.1526   $263.15   $263.15   $263.20  
  7 purchase totals = $926.48       $1,009.7636   $1,009.76   $1,009.75   $1,009.90