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 $180.43   11.776%   $201.6774   $201.68   $201.70   $201.70  
  Purchase #2 $26.71   9.821%   $29.3332   $29.33   $29.35   $29.30  
  Purchase #3 $154.46   6.429%   $164.3902   $164.39   $164.40   $164.40  
  Purchase #4 $204.66   6.508%   $217.9793   $217.98   $218.00   $218.00  
  Purchase #5 $35.55   7.821%   $38.3304   $38.33   $38.35   $38.30  
  Purchase #6 $206.95   13.499%   $234.8862   $234.89   $234.90   $234.90  
  Purchase #7 $157.92   13.496%   $179.2329   $179.23   $179.25   $179.20  
  7 purchase totals = $966.68       $1,065.8296   $1,065.83   $1,065.95   $1,065.80