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 $136.69   4.465%   $142.7932   $142.79   $142.80   $142.80  
  Purchase #2 $128.46   8.700%   $139.636   $139.64   $139.65   $139.60  
  Purchase #3 $192.37   10.233%   $212.0552   $212.06   $212.05   $212.10  
  Purchase #4 $7.71   10.499%   $8.5195   $8.52   $8.50   $8.50  
  Purchase #5 $185.87   12.844%   $209.7431   $209.74   $209.75   $209.70  
  Purchase #6 $10.50   10.848%   $11.639   $11.64   $11.65   $11.60  
  Purchase #7 $209.85   11.461%   $233.9009   $233.90   $233.90   $233.90  
  7 purchase totals = $871.45       $958.2869   $958.29   $958.30   $958.20