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 $56.31   7.789%   $60.696   $60.70   $60.70   $60.70  
  Purchase #2 $109.93   7.380%   $118.0428   $118.04   $118.05   $118.00  
  Purchase #3 $155.45   13.148%   $175.8886   $175.89   $175.90   $175.90  
  Purchase #4 $93.43   8.668%   $101.5285   $101.53   $101.55   $101.50  
  Purchase #5 $180.79   5.439%   $190.6232   $190.62   $190.60   $190.60  
  Purchase #6 $231.31   8.662%   $251.3461   $251.35   $251.35   $251.30  
  Purchase #7 $163.34   5.739%   $172.7141   $172.71   $172.70   $172.70  
  7 purchase totals = $990.56       $1,070.8393   $1,070.84   $1,070.85   $1,070.70