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 $69.96   10.568%   $77.3534   $77.35   $77.35   $77.40  
  Purchase #2 $184.80   9.706%   $202.7367   $202.74   $202.75   $202.70  
  Purchase #3 $83.52   11.398%   $93.0396   $93.04   $93.05   $93.00  
  Purchase #4 $183.35   3.623%   $189.9928   $189.99   $190.00   $190.00  
  Purchase #5 $5.38   12.229%   $6.0379   $6.04   $6.05   $6.00  
  Purchase #6 $249.95   5.179%   $262.8949   $262.89   $262.90   $262.90  
  Purchase #7 $188.73   3.159%   $194.692   $194.69   $194.70   $194.70  
  7 purchase totals = $965.69       $1,026.7473   $1,026.74   $1,026.80   $1,026.70