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 $93.59   3.488%   $96.8544   $96.85   $96.85   $96.90  
  Purchase #2 $218.93   10.145%   $241.1404   $241.14   $241.15   $241.10  
  Purchase #3 $204.90   6.652%   $218.5299   $218.53   $218.55   $218.50  
  Purchase #4 $91.34   6.160%   $96.9665   $96.97   $96.95   $97.00  
  Purchase #5 $24.35   6.821%   $26.0109   $26.01   $26.00   $26.00  
  Purchase #6 $64.42   9.702%   $70.67   $70.67   $70.65   $70.70  
  Purchase #7 $90.52   6.176%   $96.1105   $96.11   $96.10   $96.10  
  7 purchase totals = $788.05       $846.2826   $846.28   $846.25   $846.30