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 $75.53   10.489%   $83.4523   $83.45   $83.45   $83.50  
  Purchase #2 $205.95   7.604%   $221.6104   $221.61   $221.60   $221.60  
  Purchase #3 $111.93   7.210%   $120.0002   $120.00   $120.00   $120.00  
  Purchase #4 $247.79   8.799%   $269.593   $269.59   $269.60   $269.60  
  Purchase #5 $21.60   3.427%   $22.3402   $22.34   $22.35   $22.30  
  Purchase #6 $60.25   4.585%   $63.0125   $63.01   $63.00   $63.00  
  Purchase #7 $147.97   12.597%   $166.6098   $166.61   $166.60   $166.60  
  7 purchase totals = $871.02       $946.6184   $946.61   $946.60   $946.60