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 $201.62   3.363%   $208.4005   $208.40   $208.40   $208.40  
  Purchase #2 $82.75   13.543%   $93.9568   $93.96   $93.95   $94.00  
  Purchase #3 $126.82   5.770%   $134.1375   $134.14   $134.15   $134.10  
  Purchase #4 $27.34   3.459%   $28.2857   $28.29   $28.30   $28.30  
  Purchase #5 $204.65   11.558%   $228.3034   $228.30   $228.30   $228.30  
  Purchase #6 $235.96   4.383%   $246.3021   $246.30   $246.30   $246.30  
  Purchase #7 $142.51   3.713%   $147.8014   $147.80   $147.80   $147.80  
  7 purchase totals = $1,021.65       $1,087.1874   $1,087.19   $1,087.20   $1,087.20