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 $154.83   12.217%   $173.7456   $173.75   $173.75   $173.70  
  Purchase #2 $172.53   10.731%   $191.0442   $191.04   $191.05   $191.00  
  Purchase #3 $94.44   11.193%   $105.0107   $105.01   $105.00   $105.00  
  Purchase #4 $203.78   3.716%   $211.3525   $211.35   $211.35   $211.40  
  Purchase #5 $196.81   11.116%   $218.6874   $218.69   $218.70   $218.70  
  Purchase #6 $232.79   13.268%   $263.6766   $263.68   $263.70   $263.70  
  Purchase #7 $96.61   5.703%   $102.1197   $102.12   $102.10   $102.10  
  7 purchase totals = $1,151.79       $1,265.6367   $1,265.64   $1,265.65   $1,265.60