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 $148.36   7.562%   $159.579   $159.58   $159.60   $159.60  
  Purchase #2 $134.98   13.845%   $153.668   $153.67   $153.65   $153.70  
  Purchase #3 $61.67   11.267%   $68.6184   $68.62   $68.60   $68.60  
  Purchase #4 $55.36   12.827%   $62.461   $62.46   $62.45   $62.50  
  Purchase #5 $245.59   11.766%   $274.4861   $274.49   $274.50   $274.50  
  Purchase #6 $171.61   12.873%   $193.7014   $193.70   $193.70   $193.70  
  Purchase #7 $152.61   4.780%   $159.9048   $159.90   $159.90   $159.90  
  7 purchase totals = $970.18       $1,072.4187   $1,072.42   $1,072.40   $1,072.50