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 $60.76   6.352%   $64.6195   $64.62   $64.60   $64.60  
  Purchase #2 $238.47   11.811%   $266.6357   $266.64   $266.65   $266.60  
  Purchase #3 $169.82   5.692%   $179.4862   $179.49   $179.50   $179.50  
  Purchase #4 $107.92   7.681%   $116.2093   $116.21   $116.20   $116.20  
  Purchase #5 $90.95   6.510%   $96.8708   $96.87   $96.85   $96.90  
  Purchase #6 $166.32   12.774%   $187.5657   $187.57   $187.55   $187.60  
  Purchase #7 $212.53   6.320%   $225.9619   $225.96   $225.95   $226.00  
  7 purchase totals = $1,046.77       $1,137.3491   $1,137.36   $1,137.30   $1,137.40