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 $235.64   8.684%   $256.103   $256.10   $256.10   $256.10  
  Purchase #2 $50.47   6.363%   $53.6814   $53.68   $53.70   $53.70  
  Purchase #3 $92.56   6.456%   $98.5357   $98.54   $98.55   $98.50  
  Purchase #4 $192.57   7.864%   $207.7137   $207.71   $207.70   $207.70  
  Purchase #5 $203.93   4.184%   $212.4624   $212.46   $212.45   $212.50  
  Purchase #6 $231.92   11.842%   $259.384   $259.38   $259.40   $259.40  
  Purchase #7 $206.39   3.167%   $212.9264   $212.93   $212.95   $212.90  
  7 purchase totals = $1,213.48       $1,300.8066   $1,300.80   $1,300.85   $1,300.80