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 $189.91   11.266%   $211.3053   $211.31   $211.30   $211.30  
  Purchase #2 $164.95   12.366%   $185.3477   $185.35   $185.35   $185.30  
  Purchase #3 $152.32   12.601%   $171.5138   $171.51   $171.50   $171.50  
  Purchase #4 $66.77   11.671%   $74.5627   $74.56   $74.55   $74.60  
  Purchase #5 $112.29   8.547%   $121.8874   $121.89   $121.90   $121.90  
  Purchase #6 $106.60   7.569%   $114.6686   $114.67   $114.65   $114.70  
  Purchase #7 $160.90   8.252%   $174.1775   $174.18   $174.20   $174.20  
  7 purchase totals = $953.74       $1,053.4630   $1,053.47   $1,053.45   $1,053.50