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 $187.42   8.718%   $203.7593   $203.76   $203.75   $203.80  
  Purchase #2 $141.55   6.135%   $150.2341   $150.23   $150.25   $150.20  
  Purchase #3 $46.83   4.258%   $48.824   $48.82   $48.80   $48.80  
  Purchase #4 $88.32   12.233%   $99.1242   $99.12   $99.10   $99.10  
  Purchase #5 $224.54   8.142%   $242.822   $242.82   $242.80   $242.80  
  Purchase #6 $151.60   8.819%   $164.9696   $164.97   $164.95   $165.00  
  Purchase #7 $201.78   7.133%   $216.173   $216.17   $216.15   $216.20  
  7 purchase totals = $1,042.04       $1,125.9062   $1,125.89   $1,125.80   $1,125.90