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 $79.52   8.132%   $85.9866   $85.99   $86.00   $86.00  
  Purchase #2 $145.72   4.850%   $152.7874   $152.79   $152.80   $152.80  
  Purchase #3 $245.97   6.127%   $261.0406   $261.04   $261.05   $261.00  
  Purchase #4 $68.89   3.633%   $71.3928   $71.39   $71.40   $71.40  
  Purchase #5 $170.97   10.759%   $189.3647   $189.36   $189.35   $189.40  
  Purchase #6 $132.38   11.171%   $147.1682   $147.17   $147.15   $147.20  
  Purchase #7 $53.34   5.228%   $56.1286   $56.13   $56.15   $56.10  
  7 purchase totals = $896.79       $963.8689   $963.87   $963.90   $963.90