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 $195.77   13.169%   $221.551   $221.55   $221.55   $221.60  
  Purchase #2 $83.92   12.403%   $94.3286   $94.33   $94.35   $94.30  
  Purchase #3 $76.31   4.790%   $79.9652   $79.97   $79.95   $80.00  
  Purchase #4 $136.35   6.657%   $145.4268   $145.43   $145.45   $145.40  
  Purchase #5 $190.65   5.134%   $200.438   $200.44   $200.45   $200.40  
  Purchase #6 $245.80   10.126%   $270.6897   $270.69   $270.70   $270.70  
  Purchase #7 $56.50   8.676%   $61.4019   $61.40   $61.40   $61.40  
  7 purchase totals = $985.30       $1,073.8012   $1,073.81   $1,073.85   $1,073.80