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 $56.64   6.385%   $60.2565   $60.26   $60.25   $60.30  
  Purchase #2 $141.86   4.280%   $147.9316   $147.93   $147.95   $147.90  
  Purchase #3 $233.72   12.192%   $262.2151   $262.22   $262.20   $262.20  
  Purchase #4 $221.43   10.178%   $243.9671   $243.97   $243.95   $244.00  
  Purchase #5 $163.88   12.125%   $183.7505   $183.75   $183.75   $183.80  
  Purchase #6 $219.99   5.429%   $231.9333   $231.93   $231.95   $231.90  
  Purchase #7 $145.77   13.390%   $165.2886   $165.29   $165.30   $165.30  
  7 purchase totals = $1,183.29       $1,295.3427   $1,295.35   $1,295.35   $1,295.40