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 $56.28   13.826%   $64.0613   $64.06   $64.05   $64.10  
  Purchase #2 $167.36   8.163%   $181.0216   $181.02   $181.00   $181.00  
  Purchase #3 $245.63   9.835%   $269.7877   $269.79   $269.80   $269.80  
  Purchase #4 $199.96   13.671%   $227.2965   $227.30   $227.30   $227.30  
  Purchase #5 $31.56   6.708%   $33.677   $33.68   $33.70   $33.70  
  Purchase #6 $212.31   4.209%   $221.2461   $221.25   $221.25   $221.20  
  Purchase #7 $209.51   7.181%   $224.5549   $224.55   $224.55   $224.60  
  7 purchase totals = $1,122.61       $1,221.6451   $1,221.65   $1,221.65   $1,221.70