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 $184.92   4.717%   $193.6427   $193.64   $193.65   $193.60  
  Purchase #2 $248.84   4.433%   $259.8711   $259.87   $259.85   $259.90  
  Purchase #3 $19.49   13.396%   $22.1009   $22.10   $22.10   $22.10  
  Purchase #4 $154.35   7.381%   $165.7426   $165.74   $165.75   $165.70  
  Purchase #5 $239.32   10.137%   $263.5799   $263.58   $263.60   $263.60  
  Purchase #6 $148.70   5.427%   $156.7699   $156.77   $156.75   $156.80  
  Purchase #7 $180.77   12.319%   $203.0391   $203.04   $203.05   $203.00  
  7 purchase totals = $1,176.39       $1,264.7462   $1,264.74   $1,264.75   $1,264.70