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 $53.42   13.401%   $60.5788   $60.58   $60.60   $60.60  
  Purchase #2 $173.83   6.451%   $185.0438   $185.04   $185.05   $185.00  
  Purchase #3 $173.61   13.267%   $196.6428   $196.64   $196.65   $196.60  
  Purchase #4 $160.90   10.196%   $177.3054   $177.31   $177.30   $177.30  
  Purchase #5 $74.87   11.132%   $83.2045   $83.20   $83.20   $83.20  
  Purchase #6 $67.96   3.753%   $70.5105   $70.51   $70.50   $70.50  
  Purchase #7 $148.44   3.603%   $153.7883   $153.79   $153.80   $153.80  
  7 purchase totals = $853.03       $927.0741   $927.07   $927.10   $927.00