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 $138.90   9.203%   $151.683   $151.68   $151.70   $151.70  
  Purchase #2 $215.64   9.114%   $235.2934   $235.29   $235.30   $235.30  
  Purchase #3 $247.28   10.640%   $273.5906   $273.59   $273.60   $273.60  
  Purchase #4 $81.76   4.337%   $85.3059   $85.31   $85.30   $85.30  
  Purchase #5 $249.83   7.133%   $267.6504   $267.65   $267.65   $267.70  
  Purchase #6 $154.32   12.332%   $173.3507   $173.35   $173.35   $173.40  
  Purchase #7 $23.64   5.246%   $24.8802   $24.88   $24.90   $24.90  
  7 purchase totals = $1,111.37       $1,211.7542   $1,211.75   $1,211.80   $1,211.90