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 $23.70   13.205%   $26.8296   $26.83   $26.85   $26.80  
  Purchase #2 $161.87   12.723%   $182.4647   $182.46   $182.45   $182.50  
  Purchase #3 $153.75   4.561%   $160.7625   $160.76   $160.75   $160.80  
  Purchase #4 $144.60   6.125%   $153.4568   $153.46   $153.45   $153.50  
  Purchase #5 $212.57   10.264%   $234.3882   $234.39   $234.40   $234.40  
  Purchase #6 $42.29   11.409%   $47.1149   $47.11   $47.10   $47.10  
  Purchase #7 $202.74   12.136%   $227.3445   $227.34   $227.35   $227.30  
  7 purchase totals = $941.52       $1,032.3612   $1,032.35   $1,032.35   $1,032.40