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 $212.50   13.811%   $241.8484   $241.85   $241.85   $241.80  
  Purchase #2 $114.72   9.617%   $125.7526   $125.75   $125.75   $125.80  
  Purchase #3 $245.88   13.379%   $278.7763   $278.78   $278.80   $278.80  
  Purchase #4 $194.78   8.756%   $211.8349   $211.83   $211.85   $211.80  
  Purchase #5 $243.47   13.631%   $276.6574   $276.66   $276.65   $276.70  
  Purchase #6 $56.52   8.273%   $61.1959   $61.20   $61.20   $61.20  
  Purchase #7 $7.33   11.658%   $8.1845   $8.18   $8.20   $8.20  
  7 purchase totals = $1,075.20       $1,204.2500   $1,204.25   $1,204.30   $1,204.30