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 $194.82   8.789%   $211.9427   $211.94   $211.95   $211.90  
  Purchase #2 $116.29   13.379%   $131.8484   $131.85   $131.85   $131.80  
  Purchase #3 $63.37   5.769%   $67.0258   $67.03   $67.05   $67.00  
  Purchase #4 $24.80   12.729%   $27.9568   $27.96   $27.95   $28.00  
  Purchase #5 $196.78   8.510%   $213.526   $213.53   $213.55   $213.50  
  Purchase #6 $231.99   10.361%   $256.0265   $256.03   $256.05   $256.00  
  Purchase #7 $112.88   9.778%   $123.9174   $123.92   $123.90   $123.90  
  7 purchase totals = $940.93       $1,032.2436   $1,032.26   $1,032.30   $1,032.10