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 $129.42   9.137%   $141.2451   $141.25   $141.25   $141.20  
  Purchase #2 $79.93   5.857%   $84.6115   $84.61   $84.60   $84.60  
  Purchase #3 $50.95   3.631%   $52.8   $52.80   $52.80   $52.80  
  Purchase #4 $211.34   7.433%   $227.0489   $227.05   $227.05   $227.00  
  Purchase #5 $53.30   7.617%   $57.3599   $57.36   $57.35   $57.40  
  Purchase #6 $247.57   13.732%   $281.5663   $281.57   $281.55   $281.60  
  Purchase #7 $189.82   11.531%   $211.7081   $211.71   $211.70   $211.70  
  7 purchase totals = $962.33       $1,056.3398   $1,056.35   $1,056.30   $1,056.30