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 $53.84   6.211%   $57.184   $57.18   $57.20   $57.20  
  Purchase #2 $210.53   7.540%   $226.404   $226.40   $226.40   $226.40  
  Purchase #3 $92.90   12.740%   $104.7355   $104.74   $104.75   $104.70  
  Purchase #4 $143.70   9.523%   $157.3846   $157.38   $157.40   $157.40  
  Purchase #5 $223.51   11.731%   $249.73   $249.73   $249.75   $249.70  
  Purchase #6 $60.29   9.356%   $65.9307   $65.93   $65.95   $65.90  
  Purchase #7 $228.52   5.711%   $241.5708   $241.57   $241.55   $241.60  
  7 purchase totals = $1,013.29       $1,102.9396   $1,102.93   $1,103.00   $1,102.90