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 $190.74   9.671%   $209.1865   $209.19   $209.20   $209.20  
  Purchase #2 $111.57   10.163%   $122.9089   $122.91   $122.90   $122.90  
  Purchase #3 $193.52   7.407%   $207.854   $207.85   $207.85   $207.90  
  Purchase #4 $6.39   7.262%   $6.854   $6.85   $6.85   $6.90  
  Purchase #5 $144.92   8.291%   $156.9353   $156.94   $156.95   $156.90  
  Purchase #6 $180.29   12.583%   $202.9759   $202.98   $203.00   $203.00  
  Purchase #7 $96.98   9.124%   $105.8285   $105.83   $105.85   $105.80  
  7 purchase totals = $924.41       $1,012.5431   $1,012.55   $1,012.60   $1,012.60