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 $187.27   7.743%   $201.7703   $201.77   $201.75   $201.80  
  Purchase #2 $215.90   13.279%   $244.5694   $244.57   $244.55   $244.60  
  Purchase #3 $130.88   8.337%   $141.7915   $141.79   $141.80   $141.80  
  Purchase #4 $85.38   8.868%   $92.9515   $92.95   $92.95   $93.00  
  Purchase #5 $88.27   11.154%   $98.1156   $98.12   $98.10   $98.10  
  Purchase #6 $178.68   9.379%   $195.4384   $195.44   $195.45   $195.40  
  Purchase #7 $204.81   13.607%   $232.6785   $232.68   $232.70   $232.70  
  7 purchase totals = $1,091.19       $1,207.3152   $1,207.32   $1,207.30   $1,207.40