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 $96.35   12.396%   $108.2935   $108.29   $108.30   $108.30  
  Purchase #2 $176.68   9.679%   $193.7809   $193.78   $193.80   $193.80  
  Purchase #3 $81.44   4.740%   $85.3003   $85.30   $85.30   $85.30  
  Purchase #4 $91.65   3.738%   $95.0759   $95.08   $95.10   $95.10  
  Purchase #5 $20.32   11.602%   $22.6775   $22.68   $22.70   $22.70  
  Purchase #6 $207.95   7.252%   $223.0305   $223.03   $223.05   $223.00  
  Purchase #7 $14.80   12.502%   $16.6503   $16.65   $16.65   $16.70  
  7 purchase totals = $689.19       $744.8089   $744.81   $744.90   $744.90