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 $58.83   3.616%   $60.9573   $60.96   $60.95   $61.00  
  Purchase #2 $118.41   8.165%   $128.0782   $128.08   $128.10   $128.10  
  Purchase #3 $35.49   11.280%   $39.4933   $39.49   $39.50   $39.50  
  Purchase #4 $75.63   13.848%   $86.1032   $86.10   $86.10   $86.10  
  Purchase #5 $228.66   5.750%   $241.808   $241.81   $241.80   $241.80  
  Purchase #6 $112.55   12.234%   $126.3194   $126.32   $126.30   $126.30  
  Purchase #7 $77.86   12.785%   $87.8144   $87.81   $87.80   $87.80  
  7 purchase totals = $707.43       $770.5738   $770.57   $770.55   $770.60