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 $58.39   10.586%   $64.5712   $64.57   $64.55   $64.60  
  Purchase #2 $161.39   8.707%   $175.4422   $175.44   $175.45   $175.40  
  Purchase #3 $105.77   4.427%   $110.4524   $110.45   $110.45   $110.50  
  Purchase #4 $202.67   5.211%   $213.2311   $213.23   $213.25   $213.20  
  Purchase #5 $54.53   5.246%   $57.3906   $57.39   $57.40   $57.40  
  Purchase #6 $154.75   8.463%   $167.8465   $167.85   $167.85   $167.80  
  Purchase #7 $247.58   6.569%   $263.8435   $263.84   $263.85   $263.80  
  7 purchase totals = $985.08       $1,052.7775   $1,052.77   $1,052.80   $1,052.70