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 $194.98   4.493%   $203.7405   $203.74   $203.75   $203.70  
  Purchase #2 $50.73   11.543%   $56.5858   $56.59   $56.60   $56.60  
  Purchase #3 $243.25   13.817%   $276.8599   $276.86   $276.85   $276.90  
  Purchase #4 $165.40   4.185%   $172.322   $172.32   $172.30   $172.30  
  Purchase #5 $232.98   5.602%   $246.0315   $246.03   $246.05   $246.00  
  Purchase #6 $239.33   13.373%   $271.3356   $271.34   $271.35   $271.30  
  Purchase #7 $153.79   8.159%   $166.3377   $166.34   $166.35   $166.30  
  7 purchase totals = $1,280.46       $1,393.2130   $1,393.22   $1,393.25   $1,393.10