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 $171.83   6.492%   $182.9852   $182.99   $183.00   $183.00  
  Purchase #2 $94.33   12.754%   $106.3608   $106.36   $106.35   $106.40  
  Purchase #3 $32.57   12.779%   $36.7321   $36.73   $36.75   $36.70  
  Purchase #4 $233.37   3.660%   $241.9113   $241.91   $241.90   $241.90  
  Purchase #5 $194.45   4.356%   $202.9202   $202.92   $202.90   $202.90  
  Purchase #6 $194.37   11.499%   $216.7206   $216.72   $216.70   $216.70  
  Purchase #7 $163.67   7.366%   $175.7259   $175.73   $175.75   $175.70  
  7 purchase totals = $1,084.59       $1,163.3561   $1,163.36   $1,163.35   $1,163.30