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 $244.28   4.377%   $254.9721   $254.97   $254.95   $255.00  
  Purchase #2 $79.27   9.812%   $87.048   $87.05   $87.05   $87.00  
  Purchase #3 $37.67   9.425%   $41.2204   $41.22   $41.20   $41.20  
  Purchase #4 $131.70   8.243%   $142.556   $142.56   $142.55   $142.60  
  Purchase #5 $178.82   10.158%   $196.9845   $196.98   $197.00   $197.00  
  Purchase #6 $179.97   7.827%   $194.0563   $194.06   $194.05   $194.10  
  Purchase #7 $227.99   12.277%   $255.9803   $255.98   $256.00   $256.00  
  7 purchase totals = $1,079.70       $1,172.8176   $1,172.82   $1,172.80   $1,172.90