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 $55.61   9.315%   $60.7901   $60.79   $60.80   $60.80  
  Purchase #2 $216.81   10.247%   $239.0265   $239.03   $239.05   $239.00  
  Purchase #3 $246.33   7.873%   $265.7236   $265.72   $265.70   $265.70  
  Purchase #4 $46.32   9.204%   $50.5833   $50.58   $50.60   $50.60  
  Purchase #5 $179.95   13.838%   $204.8515   $204.85   $204.85   $204.90  
  Purchase #6 $215.44   13.594%   $244.7269   $244.73   $244.75   $244.70  
  Purchase #7 $175.98   7.804%   $189.7135   $189.71   $189.70   $189.70  
  7 purchase totals = $1,136.44       $1,255.4154   $1,255.41   $1,255.45   $1,255.40