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 $166.45   12.661%   $187.5242   $187.52   $187.50   $187.50  
  Purchase #2 $80.90   13.306%   $91.6646   $91.66   $91.65   $91.70  
  Purchase #3 $246.49   3.630%   $255.4376   $255.44   $255.45   $255.40  
  Purchase #4 $90.49   8.402%   $98.093   $98.09   $98.10   $98.10  
  Purchase #5 $218.97   10.366%   $241.6684   $241.67   $241.65   $241.70  
  Purchase #6 $203.48   4.755%   $213.1555   $213.16   $213.15   $213.20  
  Purchase #7 $132.93   13.562%   $150.958   $150.96   $150.95   $151.00  
  7 purchase totals = $1,139.71       $1,238.5013   $1,238.50   $1,238.45   $1,238.60