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 $241.97   8.571%   $262.7092   $262.71   $262.70   $262.70  
  Purchase #2 $39.78   10.230%   $43.8495   $43.85   $43.85   $43.80  
  Purchase #3 $64.57   9.333%   $70.5963   $70.60   $70.60   $70.60  
  Purchase #4 $130.42   13.343%   $147.8219   $147.82   $147.80   $147.80  
  Purchase #5 $149.53   8.192%   $161.7795   $161.78   $161.80   $161.80  
  Purchase #6 $157.53   4.314%   $164.3258   $164.33   $164.35   $164.30  
  Purchase #7 $9.25   7.848%   $9.9759   $9.98   $10.00   $10.00  
  7 purchase totals = $793.05       $861.0581   $861.07   $861.10   $861.00