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 $241.47   5.213%   $254.0578   $254.06   $254.05   $254.10  
  Purchase #2 $88.90   8.404%   $96.3712   $96.37   $96.35   $96.40  
  Purchase #3 $92.44   6.500%   $98.4486   $98.45   $98.45   $98.40  
  Purchase #4 $25.60   3.556%   $26.5103   $26.51   $26.50   $26.50  
  Purchase #5 $214.70   5.133%   $225.7206   $225.72   $225.70   $225.70  
  Purchase #6 $68.87   7.462%   $74.0091   $74.01   $74.00   $74.00  
  Purchase #7 $68.43   3.250%   $70.654   $70.65   $70.65   $70.70  
  7 purchase totals = $800.41       $845.7716   $845.77   $845.70   $845.80