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 $244.85   12.448%   $275.3289   $275.33   $275.35   $275.30  
  Purchase #2 $12.92   8.534%   $14.0226   $14.02   $14.00   $14.00  
  Purchase #3 $192.29   5.461%   $202.791   $202.79   $202.80   $202.80  
  Purchase #4 $127.54   10.816%   $141.3347   $141.33   $141.35   $141.30  
  Purchase #5 $60.72   11.739%   $67.8479   $67.85   $67.85   $67.80  
  Purchase #6 $105.81   10.390%   $116.8037   $116.80   $116.80   $116.80  
  Purchase #7 $190.97   7.686%   $205.648   $205.65   $205.65   $205.60  
  7 purchase totals = $935.10       $1,023.7768   $1,023.77   $1,023.80   $1,023.60