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 $60.85   12.452%   $68.427   $68.43   $68.45   $68.40  
  Purchase #2 $213.60   4.828%   $223.9126   $223.91   $223.90   $223.90  
  Purchase #3 $236.26   9.104%   $257.7691   $257.77   $257.75   $257.80  
  Purchase #4 $202.61   4.232%   $211.1845   $211.18   $211.20   $211.20  
  Purchase #5 $86.91   4.159%   $90.5246   $90.52   $90.50   $90.50  
  Purchase #6 $210.26   8.639%   $228.4244   $228.42   $228.40   $228.40  
  Purchase #7 $240.52   3.169%   $248.1421   $248.14   $248.15   $248.10  
  7 purchase totals = $1,251.01       $1,328.3843   $1,328.37   $1,328.35   $1,328.30