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 $233.62   8.834%   $254.258   $254.26   $254.25   $254.30  
  Purchase #2 $53.86   7.712%   $58.0137   $58.01   $58.00   $58.00  
  Purchase #3 $117.38   8.302%   $127.1249   $127.12   $127.10   $127.10  
  Purchase #4 $113.81   10.592%   $125.8648   $125.86   $125.85   $125.90  
  Purchase #5 $150.92   13.659%   $171.5342   $171.53   $171.55   $171.50  
  Purchase #6 $212.26   8.821%   $230.9835   $230.98   $231.00   $231.00  
  Purchase #7 $188.28   10.412%   $207.8837   $207.88   $207.90   $207.90  
  7 purchase totals = $1,070.13       $1,175.6628   $1,175.64   $1,175.65   $1,175.70