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 $123.54   10.342%   $136.3165   $136.32   $136.30   $136.30  
  Purchase #2 $166.97   5.217%   $175.6808   $175.68   $175.70   $175.70  
  Purchase #3 $88.63   10.113%   $97.5932   $97.59   $97.60   $97.60  
  Purchase #4 $187.27   10.292%   $206.5438   $206.54   $206.55   $206.50  
  Purchase #5 $118.87   4.644%   $124.3903   $124.39   $124.40   $124.40  
  Purchase #6 $204.98   7.133%   $219.6012   $219.60   $219.60   $219.60  
  Purchase #7 $81.29   5.610%   $85.8504   $85.85   $85.85   $85.90  
  7 purchase totals = $971.55       $1,045.9762   $1,045.97   $1,046.00   $1,046.00