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 $85.37   13.824%   $97.1715   $97.17   $97.15   $97.20  
  Purchase #2 $96.51   7.413%   $103.6643   $103.66   $103.65   $103.70  
  Purchase #3 $145.55   7.297%   $156.1708   $156.17   $156.15   $156.20  
  Purchase #4 $65.57   7.155%   $70.2615   $70.26   $70.25   $70.30  
  Purchase #5 $227.84   7.844%   $245.7118   $245.71   $245.70   $245.70  
  Purchase #6 $201.31   13.866%   $229.2236   $229.22   $229.20   $229.20  
  Purchase #7 $203.48   6.598%   $216.9056   $216.91   $216.90   $216.90  
  7 purchase totals = $1,025.63       $1,119.1091   $1,119.10   $1,119.00   $1,119.20