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 $88.63   11.744%   $99.0387   $99.04   $99.05   $99.00  
  Purchase #2 $92.41   10.311%   $101.9384   $101.94   $101.95   $101.90  
  Purchase #3 $219.38   10.117%   $241.5747   $241.57   $241.55   $241.60  
  Purchase #4 $229.29   6.864%   $245.0285   $245.03   $245.05   $245.00  
  Purchase #5 $158.87   6.169%   $168.6707   $168.67   $168.65   $168.70  
  Purchase #6 $179.36   12.576%   $201.9163   $201.92   $201.90   $201.90  
  Purchase #7 $127.30   5.362%   $134.1258   $134.13   $134.15   $134.10  
  7 purchase totals = $1,095.24       $1,192.2931   $1,192.30   $1,192.30   $1,192.20