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 $215.84   7.834%   $232.7489   $232.75   $232.75   $232.70  
  Purchase #2 $165.68   4.279%   $172.7694   $172.77   $172.75   $172.80  
  Purchase #3 $23.80   9.157%   $25.9794   $25.98   $26.00   $26.00  
  Purchase #4 $88.69   8.602%   $96.3191   $96.32   $96.30   $96.30  
  Purchase #5 $19.88   6.871%   $21.246   $21.25   $21.25   $21.20  
  Purchase #6 $156.50   8.336%   $169.5458   $169.55   $169.55   $169.50  
  Purchase #7 $101.40   4.814%   $106.2814   $106.28   $106.30   $106.30  
  7 purchase totals = $771.79       $824.8900   $824.90   $824.90   $824.80