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 $250.44   4.757%   $262.3534   $262.35   $262.35   $262.40  
  Purchase #2 $132.61   7.585%   $142.6685   $142.67   $142.65   $142.70  
  Purchase #3 $223.32   5.648%   $235.9331   $235.93   $235.95   $235.90  
  Purchase #4 $244.61   5.438%   $257.9119   $257.91   $257.90   $257.90  
  Purchase #5 $157.60   11.731%   $176.0881   $176.09   $176.10   $176.10  
  Purchase #6 $204.60   11.454%   $228.0349   $228.03   $228.05   $228.00  
  Purchase #7 $28.45   10.489%   $31.4341   $31.43   $31.45   $31.40  
  7 purchase totals = $1,241.63       $1,334.4240   $1,334.41   $1,334.45   $1,334.40