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 $56.57   8.673%   $61.4763   $61.48   $61.50   $61.50  
  Purchase #2 $134.76   13.426%   $152.8529   $152.85   $152.85   $152.90  
  Purchase #3 $87.63   10.556%   $96.8802   $96.88   $96.90   $96.90  
  Purchase #4 $179.66   8.279%   $194.5341   $194.53   $194.55   $194.50  
  Purchase #5 $157.68   12.523%   $177.4263   $177.43   $177.45   $177.40  
  Purchase #6 $178.52   3.160%   $184.1612   $184.16   $184.15   $184.20  
  Purchase #7 $132.49   7.751%   $142.7593   $142.76   $142.75   $142.80  
  7 purchase totals = $927.31       $1,010.0903   $1,010.09   $1,010.15   $1,010.20