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 $90.54   3.821%   $93.9995   $94.00   $94.00   $94.00  
  Purchase #2 $171.71   9.683%   $188.3367   $188.34   $188.35   $188.30  
  Purchase #3 $15.86   5.139%   $16.675   $16.68   $16.70   $16.70  
  Purchase #4 $110.52   6.271%   $117.4507   $117.45   $117.45   $117.50  
  Purchase #5 $204.40   4.463%   $213.5224   $213.52   $213.50   $213.50  
  Purchase #6 $245.66   6.162%   $260.7976   $260.80   $260.80   $260.80  
  Purchase #7 $220.39   8.596%   $239.3347   $239.33   $239.35   $239.30  
  7 purchase totals = $1,059.08       $1,130.1166   $1,130.12   $1,130.15   $1,130.10