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 $49.27   13.819%   $56.0786   $56.08   $56.10   $56.10  
  Purchase #2 $174.84   3.683%   $181.2794   $181.28   $181.30   $181.30  
  Purchase #3 $124.53   6.516%   $132.6444   $132.64   $132.65   $132.60  
  Purchase #4 $207.86   3.394%   $214.9148   $214.91   $214.90   $214.90  
  Purchase #5 $93.43   11.810%   $104.4641   $104.46   $104.45   $104.50  
  Purchase #6 $130.48   6.450%   $138.896   $138.90   $138.90   $138.90  
  Purchase #7 $160.72   9.129%   $175.3921   $175.39   $175.40   $175.40  
  7 purchase totals = $941.13       $1,003.6694   $1,003.66   $1,003.70   $1,003.70