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 $173.59   13.118%   $196.3615   $196.36   $196.35   $196.40  
  Purchase #2 $20.70   8.258%   $22.4094   $22.41   $22.40   $22.40  
  Purchase #3 $166.72   12.274%   $187.1832   $187.18   $187.20   $187.20  
  Purchase #4 $241.44   11.502%   $269.2104   $269.21   $269.20   $269.20  
  Purchase #5 $105.34   10.120%   $116.0004   $116.00   $116.00   $116.00  
  Purchase #6 $210.30   7.114%   $225.2607   $225.26   $225.25   $225.30  
  Purchase #7 $145.96   6.538%   $155.5029   $155.50   $155.50   $155.50  
  7 purchase totals = $1,064.05       $1,171.9285   $1,171.92   $1,171.90   $1,172.00