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 $69.29   8.529%   $75.1997   $75.20   $75.20   $75.20  
  Purchase #2 $134.90   9.503%   $147.7195   $147.72   $147.70   $147.70  
  Purchase #3 $168.82   5.602%   $178.2773   $178.28   $178.30   $178.30  
  Purchase #4 $26.56   12.461%   $29.8696   $29.87   $29.85   $29.90  
  Purchase #5 $78.52   12.291%   $88.1709   $88.17   $88.15   $88.20  
  Purchase #6 $91.52   8.298%   $99.1143   $99.11   $99.10   $99.10  
  Purchase #7 $177.45   3.592%   $183.824   $183.82   $183.80   $183.80  
  7 purchase totals = $747.06       $802.1753   $802.17   $802.10   $802.20