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 $44.43   11.734%   $49.6434   $49.64   $49.65   $49.60  
  Purchase #2 $100.40   7.547%   $107.9772   $107.98   $108.00   $108.00  
  Purchase #3 $187.61   13.324%   $212.6072   $212.61   $212.60   $212.60  
  Purchase #4 $39.25   9.515%   $42.9846   $42.98   $43.00   $43.00  
  Purchase #5 $9.59   5.113%   $10.0803   $10.08   $10.10   $10.10  
  Purchase #6 $16.42   7.287%   $17.6165   $17.62   $17.60   $17.60  
  Purchase #7 $120.69   5.102%   $126.8476   $126.85   $126.85   $126.80  
  7 purchase totals = $518.39       $567.7568   $567.76   $567.80   $567.70