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 $84.57   8.694%   $91.9225   $91.92   $91.90   $91.90  
  Purchase #2 $241.49   5.470%   $254.6995   $254.70   $254.70   $254.70  
  Purchase #3 $79.77   10.313%   $87.9967   $88.00   $88.00   $88.00  
  Purchase #4 $165.46   11.837%   $185.0455   $185.05   $185.05   $185.00  
  Purchase #5 $157.42   4.857%   $165.0659   $165.07   $165.05   $165.10  
  Purchase #6 $38.26   13.845%   $43.5571   $43.56   $43.55   $43.60  
  Purchase #7 $185.84   6.747%   $198.3786   $198.38   $198.40   $198.40  
  7 purchase totals = $952.81       $1,026.6658   $1,026.68   $1,026.65   $1,026.70