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 $49.35   11.571%   $55.0603   $55.06   $55.05   $55.10  
  Purchase #2 $201.85   11.689%   $225.4442   $225.44   $225.45   $225.40  
  Purchase #3 $53.88   13.547%   $61.1791   $61.18   $61.20   $61.20  
  Purchase #4 $192.85   5.348%   $203.1636   $203.16   $203.15   $203.20  
  Purchase #5 $145.26   10.156%   $160.0126   $160.01   $160.00   $160.00  
  Purchase #6 $126.36   11.662%   $141.0961   $141.10   $141.10   $141.10  
  Purchase #7 $241.69   6.661%   $257.789   $257.79   $257.80   $257.80  
  7 purchase totals = $1,011.24       $1,103.7449   $1,103.74   $1,103.75   $1,103.80