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 $102.77   11.448%   $114.5351   $114.54   $114.55   $114.50  
  Purchase #2 $183.73   9.153%   $200.5468   $200.55   $200.55   $200.50  
  Purchase #3 $243.27   8.511%   $263.9747   $263.97   $263.95   $264.00  
  Purchase #4 $113.70   8.354%   $123.1985   $123.20   $123.20   $123.20  
  Purchase #5 $33.92   7.764%   $36.5535   $36.55   $36.55   $36.60  
  Purchase #6 $184.50   7.753%   $198.8043   $198.80   $198.80   $198.80  
  Purchase #7 $228.82   11.598%   $255.3585   $255.36   $255.35   $255.40  
  7 purchase totals = $1,090.71       $1,192.9714   $1,192.97   $1,192.95   $1,193.00