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 $93.28   3.691%   $96.723   $96.72   $96.70   $96.70  
  Purchase #2 $227.52   11.215%   $253.0364   $253.04   $253.05   $253.00  
  Purchase #3 $18.51   7.142%   $19.832   $19.83   $19.85   $19.80  
  Purchase #4 $114.73   7.801%   $123.6801   $123.68   $123.70   $123.70  
  Purchase #5 $108.57   3.662%   $112.5458   $112.55   $112.55   $112.50  
  Purchase #6 $112.33   5.351%   $118.3408   $118.34   $118.35   $118.30  
  Purchase #7 $202.71   11.575%   $226.1737   $226.17   $226.15   $226.20  
  7 purchase totals = $877.65       $950.3318   $950.33   $950.35   $950.20