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 $46.26   13.107%   $52.3233   $52.32   $52.30   $52.30  
  Purchase #2 $203.84   13.499%   $231.3564   $231.36   $231.35   $231.40  
  Purchase #3 $231.47   10.270%   $255.242   $255.24   $255.25   $255.20  
  Purchase #4 $227.94   10.337%   $251.5022   $251.50   $251.50   $251.50  
  Purchase #5 $63.86   3.288%   $65.9597   $65.96   $65.95   $66.00  
  Purchase #6 $100.41   5.792%   $106.2257   $106.23   $106.25   $106.20  
  Purchase #7 $167.88   8.847%   $182.7323   $182.73   $182.75   $182.70  
  7 purchase totals = $1,041.66       $1,145.3416   $1,145.34   $1,145.35   $1,145.30