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 $54.25   4.465%   $56.6723   $56.67   $56.65   $56.70  
  Purchase #2 $24.51   6.633%   $26.1357   $26.14   $26.15   $26.10  
  Purchase #3 $134.60   12.160%   $150.9674   $150.97   $150.95   $151.00  
  Purchase #4 $249.26   11.590%   $278.1492   $278.15   $278.15   $278.10  
  Purchase #5 $183.84   4.205%   $191.5705   $191.57   $191.55   $191.60  
  Purchase #6 $249.52   5.493%   $263.2261   $263.23   $263.25   $263.20  
  Purchase #7 $201.72   6.266%   $214.3598   $214.36   $214.35   $214.40  
  7 purchase totals = $1,097.70       $1,181.0810   $1,181.09   $1,181.05   $1,181.10