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 $5.43   9.460%   $5.9437   $5.94   $5.95   $5.90  
  Purchase #2 $186.64   10.121%   $205.5298   $205.53   $205.55   $205.50  
  Purchase #3 $85.81   11.632%   $95.7914   $95.79   $95.80   $95.80  
  Purchase #4 $124.84   10.405%   $137.8296   $137.83   $137.85   $137.80  
  Purchase #5 $246.86   4.461%   $257.8724   $257.87   $257.85   $257.90  
  Purchase #6 $209.51   11.803%   $234.2385   $234.24   $234.25   $234.20  
  Purchase #7 $91.33   7.320%   $98.0154   $98.02   $98.00   $98.00  
  7 purchase totals = $950.42       $1,035.2208   $1,035.22   $1,035.25   $1,035.10