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 $181.96   9.114%   $198.5438   $198.54   $198.55   $198.50  
  Purchase #2 $234.99   7.170%   $251.8388   $251.84   $251.85   $251.80  
  Purchase #3 $151.34   7.239%   $162.2955   $162.30   $162.30   $162.30  
  Purchase #4 $155.91   7.280%   $167.2602   $167.26   $167.25   $167.30  
  Purchase #5 $124.88   9.421%   $136.6449   $136.64   $136.65   $136.60  
  Purchase #6 $138.74   4.355%   $144.7821   $144.78   $144.80   $144.80  
  Purchase #7 $192.27   7.821%   $207.3074   $207.31   $207.30   $207.30  
  7 purchase totals = $1,180.09       $1,268.6727   $1,268.67   $1,268.70   $1,268.60