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 $174.84   6.491%   $186.1889   $186.19   $186.20   $186.20  
  Purchase #2 $208.36   3.454%   $215.5568   $215.56   $215.55   $215.60  
  Purchase #3 $226.75   11.588%   $253.0258   $253.03   $253.05   $253.00  
  Purchase #4 $25.83   12.144%   $28.9668   $28.97   $28.95   $29.00  
  Purchase #5 $246.99   9.324%   $270.0193   $270.02   $270.00   $270.00  
  Purchase #6 $76.26   11.871%   $85.3128   $85.31   $85.30   $85.30  
  Purchase #7 $218.99   6.179%   $232.5214   $232.52   $232.50   $232.50  
  7 purchase totals = $1,178.02       $1,271.5918   $1,271.60   $1,271.55   $1,271.60