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 $69.89   8.439%   $75.788   $75.79   $75.80   $75.80  
  Purchase #2 $166.71   7.670%   $179.4967   $179.50   $179.50   $179.50  
  Purchase #3 $200.52   11.535%   $223.65   $223.65   $223.65   $223.70  
  Purchase #4 $190.52   7.632%   $205.0605   $205.06   $205.05   $205.10  
  Purchase #5 $61.64   8.767%   $67.044   $67.04   $67.05   $67.00  
  Purchase #6 $205.92   4.103%   $214.3689   $214.37   $214.35   $214.40  
  Purchase #7 $210.97   10.674%   $233.4889   $233.49   $233.50   $233.50  
  7 purchase totals = $1,106.17       $1,198.8970   $1,198.90   $1,198.90   $1,199.00