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 $216.95   5.297%   $228.4418   $228.44   $228.45   $228.40  
  Purchase #2 $168.75   4.685%   $176.6559   $176.66   $176.65   $176.70  
  Purchase #3 $77.84   4.201%   $81.1101   $81.11   $81.10   $81.10  
  Purchase #4 $77.80   5.403%   $82.0035   $82.00   $82.00   $82.00  
  Purchase #5 $98.62   4.671%   $103.2265   $103.23   $103.25   $103.20  
  Purchase #6 $181.70   12.144%   $203.7656   $203.77   $203.75   $203.80  
  Purchase #7 $196.76   3.576%   $203.7961   $203.80   $203.80   $203.80  
  7 purchase totals = $1,018.42       $1,078.9995   $1,079.01   $1,079.00   $1,079.00