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 $85.93   11.852%   $96.1144   $96.11   $96.10   $96.10  
  Purchase #2 $184.47   5.352%   $194.3428   $194.34   $194.35   $194.30  
  Purchase #3 $233.44   9.211%   $254.9422   $254.94   $254.95   $254.90  
  Purchase #4 $27.74   4.167%   $28.8959   $28.90   $28.90   $28.90  
  Purchase #5 $146.29   4.849%   $153.3836   $153.38   $153.40   $153.40  
  Purchase #6 $172.39   12.149%   $193.3337   $193.33   $193.35   $193.30  
  Purchase #7 $219.84   4.462%   $229.6493   $229.65   $229.65   $229.60  
  7 purchase totals = $1,070.10       $1,150.6619   $1,150.65   $1,150.70   $1,150.50