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 $85.90   11.793%   $96.0302   $96.03   $96.05   $96.00  
  Purchase #2 $144.35   10.729%   $159.8373   $159.84   $159.85   $159.80  
  Purchase #3 $179.53   13.767%   $204.2459   $204.25   $204.25   $204.20  
  Purchase #4 $91.74   9.127%   $100.1131   $100.11   $100.10   $100.10  
  Purchase #5 $22.78   5.714%   $24.0816   $24.08   $24.10   $24.10  
  Purchase #6 $11.60   5.568%   $12.2459   $12.25   $12.25   $12.20  
  Purchase #7 $247.77   9.164%   $270.4756   $270.48   $270.50   $270.50  
  7 purchase totals = $783.67       $867.0296   $867.04   $867.10   $866.90