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 $94.63   3.459%   $97.9033   $97.90   $97.90   $97.90  
  Purchase #2 $184.81   9.109%   $201.6443   $201.64   $201.65   $201.60  
  Purchase #3 $169.53   4.627%   $177.3742   $177.37   $177.35   $177.40  
  Purchase #4 $161.52   9.506%   $176.8741   $176.87   $176.85   $176.90  
  Purchase #5 $83.31   10.303%   $91.8934   $91.89   $91.90   $91.90  
  Purchase #6 $230.66   8.217%   $249.6133   $249.61   $249.60   $249.60  
  Purchase #7 $54.86   5.778%   $58.0298   $58.03   $58.05   $58.00  
  7 purchase totals = $979.32       $1,053.3324   $1,053.31   $1,053.30   $1,053.30