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 $234.53   5.830%   $248.2031   $248.20   $248.20   $248.20  
  Purchase #2 $176.65   9.370%   $193.2021   $193.20   $193.20   $193.20  
  Purchase #3 $197.70   6.726%   $210.9973   $211.00   $211.00   $211.00  
  Purchase #4 $204.57   3.510%   $211.7504   $211.75   $211.75   $211.80  
  Purchase #5 $210.59   7.519%   $226.4243   $226.42   $226.40   $226.40  
  Purchase #6 $202.64   10.829%   $224.5839   $224.58   $224.60   $224.60  
  Purchase #7 $64.56   4.539%   $67.4904   $67.49   $67.50   $67.50  
  7 purchase totals = $1,291.24       $1,382.6515   $1,382.64   $1,382.65   $1,382.70