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 $177.26   11.145%   $197.0156   $197.02   $197.00   $197.00  
  Purchase #2 $146.47   3.265%   $151.2522   $151.25   $151.25   $151.30  
  Purchase #3 $30.87   11.615%   $34.4556   $34.46   $34.45   $34.50  
  Purchase #4 $220.75   9.467%   $241.6484   $241.65   $241.65   $241.60  
  Purchase #5 $84.44   12.357%   $94.8743   $94.87   $94.85   $94.90  
  Purchase #6 $23.91   7.644%   $25.7377   $25.74   $25.75   $25.70  
  Purchase #7 $72.62   3.444%   $75.121   $75.12   $75.10   $75.10  
  7 purchase totals = $756.32       $820.1048   $820.11   $820.05   $820.10