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 $147.92   13.350%   $167.6673   $167.67   $167.65   $167.70  
  Purchase #2 $166.30   12.230%   $186.6385   $186.64   $186.65   $186.60  
  Purchase #3 $243.83   4.121%   $253.8782   $253.88   $253.90   $253.90  
  Purchase #4 $64.43   9.783%   $70.7332   $70.73   $70.75   $70.70  
  Purchase #5 $103.54   6.624%   $110.3985   $110.40   $110.40   $110.40  
  Purchase #6 $167.81   11.543%   $187.1803   $187.18   $187.20   $187.20  
  Purchase #7 $50.56   11.575%   $56.4123   $56.41   $56.40   $56.40  
  7 purchase totals = $944.39       $1,032.9083   $1,032.91   $1,032.95   $1,032.90