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 $211.47   12.870%   $238.6862   $238.69   $238.70   $238.70  
  Purchase #2 $226.42   6.375%   $240.8543   $240.85   $240.85   $240.90  
  Purchase #3 $55.45   10.147%   $61.0765   $61.08   $61.10   $61.10  
  Purchase #4 $193.48   9.445%   $211.7542   $211.75   $211.75   $211.80  
  Purchase #5 $219.29   12.794%   $247.346   $247.35   $247.35   $247.30  
  Purchase #6 $30.33   13.378%   $34.3875   $34.39   $34.40   $34.40  
  Purchase #7 $109.49   5.849%   $115.8941   $115.89   $115.90   $115.90  
  7 purchase totals = $1,045.93       $1,149.9988   $1,150.00   $1,150.05   $1,150.10