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 $232.86   9.800%   $255.6803   $255.68   $255.70   $255.70  
  Purchase #2 $114.75   3.653%   $118.9418   $118.94   $118.95   $118.90  
  Purchase #3 $128.82   11.647%   $143.8237   $143.82   $143.80   $143.80  
  Purchase #4 $141.62   11.164%   $157.4305   $157.43   $157.45   $157.40  
  Purchase #5 $238.89   3.415%   $247.0481   $247.05   $247.05   $247.00  
  Purchase #6 $207.32   4.514%   $216.6784   $216.68   $216.70   $216.70  
  Purchase #7 $58.69   11.361%   $65.3578   $65.36   $65.35   $65.40  
  7 purchase totals = $1,122.95       $1,204.9606   $1,204.96   $1,205.00   $1,204.90