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 $244.92   11.596%   $273.3209   $273.32   $273.30   $273.30  
  Purchase #2 $189.89   4.107%   $197.6888   $197.69   $197.70   $197.70  
  Purchase #3 $131.70   11.864%   $147.3249   $147.32   $147.30   $147.30  
  Purchase #4 $225.68   5.784%   $238.7333   $238.73   $238.75   $238.70  
  Purchase #5 $215.96   4.453%   $225.5767   $225.58   $225.60   $225.60  
  Purchase #6 $106.73   8.202%   $115.484   $115.48   $115.50   $115.50  
  Purchase #7 $49.49   9.497%   $54.1901   $54.19   $54.20   $54.20  
  7 purchase totals = $1,164.37       $1,252.3187   $1,252.31   $1,252.35   $1,252.30