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 $85.41   12.286%   $95.9035   $95.90   $95.90   $95.90  
  Purchase #2 $205.85   3.656%   $213.3759   $213.38   $213.40   $213.40  
  Purchase #3 $53.91   5.121%   $56.6707   $56.67   $56.65   $56.70  
  Purchase #4 $157.85   6.402%   $167.9556   $167.96   $167.95   $168.00  
  Purchase #5 $85.34   13.280%   $96.6732   $96.67   $96.65   $96.70  
  Purchase #6 $230.58   12.842%   $260.1911   $260.19   $260.20   $260.20  
  Purchase #7 $105.28   11.570%   $117.4609   $117.46   $117.45   $117.50  
  7 purchase totals = $924.22       $1,008.2309   $1,008.23   $1,008.20   $1,008.40