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 $231.25   8.518%   $250.9479   $250.95   $250.95   $250.90  
  Purchase #2 $247.82   12.712%   $279.3229   $279.32   $279.30   $279.30  
  Purchase #3 $33.91   8.565%   $36.8144   $36.81   $36.80   $36.80  
  Purchase #4 $68.87   6.406%   $73.2818   $73.28   $73.30   $73.30  
  Purchase #5 $45.72   8.224%   $49.48   $49.48   $49.50   $49.50  
  Purchase #6 $159.56   12.408%   $179.3582   $179.36   $179.35   $179.40  
  Purchase #7 $201.27   12.687%   $226.8051   $226.81   $226.80   $226.80  
  7 purchase totals = $988.40       $1,096.0103   $1,096.01   $1,096.00   $1,096.00