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 $171.32   8.544%   $185.9576   $185.96   $185.95   $186.00  
  Purchase #2 $218.41   7.754%   $235.3455   $235.35   $235.35   $235.30  
  Purchase #3 $209.65   5.285%   $220.73   $220.73   $220.75   $220.70  
  Purchase #4 $133.95   10.443%   $147.9384   $147.94   $147.95   $147.90  
  Purchase #5 $17.30   9.207%   $18.8928   $18.89   $18.90   $18.90  
  Purchase #6 $189.74   12.838%   $214.0988   $214.10   $214.10   $214.10  
  Purchase #7 $143.30   4.830%   $150.2214   $150.22   $150.20   $150.20  
  7 purchase totals = $1,083.67       $1,173.1845   $1,173.19   $1,173.20   $1,173.10