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 $55.76   9.779%   $61.2128   $61.21   $61.20   $61.20  
  Purchase #2 $32.85   12.233%   $36.8685   $36.87   $36.85   $36.90  
  Purchase #3 $22.64   9.293%   $24.7439   $24.74   $24.75   $24.70  
  Purchase #4 $244.41   6.356%   $259.9447   $259.94   $259.95   $259.90  
  Purchase #5 $212.50   9.658%   $233.0233   $233.02   $233.00   $233.00  
  Purchase #6 $241.66   11.196%   $268.7163   $268.72   $268.70   $268.70  
  Purchase #7 $214.44   8.346%   $232.3372   $232.34   $232.35   $232.30  
  7 purchase totals = $1,024.26       $1,116.8467   $1,116.84   $1,116.80   $1,116.70