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 $212.67   6.510%   $226.5148   $226.51   $226.50   $226.50  
  Purchase #2 $160.39   3.713%   $166.3453   $166.35   $166.35   $166.30  
  Purchase #3 $39.50   10.373%   $43.5973   $43.60   $43.60   $43.60  
  Purchase #4 $175.48   13.215%   $198.6697   $198.67   $198.65   $198.70  
  Purchase #5 $218.94   3.469%   $226.535   $226.54   $226.55   $226.50  
  Purchase #6 $161.77   4.497%   $169.0448   $169.04   $169.05   $169.00  
  Purchase #7 $160.28   4.134%   $166.906   $166.91   $166.90   $166.90  
  7 purchase totals = $1,129.03       $1,197.6129   $1,197.62   $1,197.60   $1,197.50