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 $206.46   5.759%   $218.35   $218.35   $218.35   $218.40  
  Purchase #2 $75.86   7.374%   $81.4539   $81.45   $81.45   $81.50  
  Purchase #3 $163.95   8.619%   $178.0809   $178.08   $178.10   $178.10  
  Purchase #4 $242.90   9.453%   $265.8613   $265.86   $265.85   $265.90  
  Purchase #5 $121.32   7.740%   $130.7102   $130.71   $130.70   $130.70  
  Purchase #6 $166.94   8.767%   $181.5756   $181.58   $181.60   $181.60  
  Purchase #7 $44.89   8.357%   $48.6415   $48.64   $48.65   $48.60  
  7 purchase totals = $1,022.32       $1,104.6734   $1,104.67   $1,104.70   $1,104.80