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 $53.92   11.612%   $60.1812   $60.18   $60.20   $60.20  
  Purchase #2 $218.85   9.251%   $239.0958   $239.10   $239.10   $239.10  
  Purchase #3 $35.26   6.230%   $37.4567   $37.46   $37.45   $37.50  
  Purchase #4 $72.81   7.770%   $78.4673   $78.47   $78.45   $78.50  
  Purchase #5 $181.97   11.667%   $203.2004   $203.20   $203.20   $203.20  
  Purchase #6 $194.64   9.422%   $212.979   $212.98   $213.00   $213.00  
  Purchase #7 $38.93   4.310%   $40.6079   $40.61   $40.60   $40.60  
  7 purchase totals = $796.38       $871.9883   $872.00   $872.00   $872.10