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 $194.39   6.338%   $206.7104   $206.71   $206.70   $206.70  
  Purchase #2 $73.93   9.162%   $80.7035   $80.70   $80.70   $80.70  
  Purchase #3 $233.54   9.242%   $255.1238   $255.12   $255.10   $255.10  
  Purchase #4 $23.92   11.201%   $26.5993   $26.60   $26.60   $26.60  
  Purchase #5 $22.74   10.682%   $25.1691   $25.17   $25.15   $25.20  
  Purchase #6 $172.70   13.235%   $195.5568   $195.56   $195.55   $195.60  
  Purchase #7 $226.53   7.598%   $243.7417   $243.74   $243.75   $243.70  
  7 purchase totals = $947.75       $1,033.6046   $1,033.60   $1,033.55   $1,033.60