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 $133.75   8.597%   $145.2485   $145.25   $145.25   $145.20  
  Purchase #2 $237.96   6.595%   $253.6535   $253.65   $253.65   $253.70  
  Purchase #3 $58.34   6.697%   $62.247   $62.25   $62.25   $62.20  
  Purchase #4 $241.84   11.414%   $269.4436   $269.44   $269.45   $269.40  
  Purchase #5 $234.52   6.566%   $249.9186   $249.92   $249.90   $249.90  
  Purchase #6 $5.31   10.862%   $5.8868   $5.89   $5.90   $5.90  
  Purchase #7 $82.33   11.793%   $92.0392   $92.04   $92.05   $92.00  
  7 purchase totals = $994.05       $1,078.4372   $1,078.44   $1,078.45   $1,078.30