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 $24.37   7.662%   $26.2372   $26.24   $26.25   $26.20  
  Purchase #2 $211.37   9.135%   $230.6786   $230.68   $230.70   $230.70  
  Purchase #3 $160.46   8.146%   $173.5311   $173.53   $173.55   $173.50  
  Purchase #4 $181.32   12.121%   $203.2978   $203.30   $203.30   $203.30  
  Purchase #5 $75.41   10.846%   $83.589   $83.59   $83.60   $83.60  
  Purchase #6 $109.34   6.231%   $116.153   $116.15   $116.15   $116.20  
  Purchase #7 $20.63   6.690%   $22.0101   $22.01   $22.00   $22.00  
  7 purchase totals = $782.90       $855.4968   $855.50   $855.55   $855.50