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 $244.34   7.160%   $261.8347   $261.83   $261.85   $261.80  
  Purchase #2 $102.96   12.671%   $116.0061   $116.01   $116.00   $116.00  
  Purchase #3 $7.69   6.363%   $8.1793   $8.18   $8.20   $8.20  
  Purchase #4 $45.71   11.565%   $50.9964   $51.00   $51.00   $51.00  
  Purchase #5 $220.74   4.239%   $230.0972   $230.10   $230.10   $230.10  
  Purchase #6 $246.30   10.702%   $272.659   $272.66   $272.65   $272.70  
  Purchase #7 $118.62   7.297%   $127.2757   $127.28   $127.30   $127.30  
  7 purchase totals = $986.36       $1,067.0484   $1,067.06   $1,067.10   $1,067.10