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 $132.99   13.237%   $150.5939   $150.59   $150.60   $150.60  
  Purchase #2 $135.30   3.214%   $139.6485   $139.65   $139.65   $139.60  
  Purchase #3 $67.31   4.230%   $70.1572   $70.16   $70.15   $70.20  
  Purchase #4 $162.32   7.806%   $174.9907   $174.99   $175.00   $175.00  
  Purchase #5 $178.29   11.357%   $198.5384   $198.54   $198.55   $198.50  
  Purchase #6 $220.75   10.793%   $244.5755   $244.58   $244.60   $244.60  
  Purchase #7 $42.66   10.644%   $47.2007   $47.20   $47.20   $47.20  
  7 purchase totals = $939.62       $1,025.7049   $1,025.71   $1,025.75   $1,025.70