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 $214.42   8.168%   $231.9338   $231.93   $231.95   $231.90  
  Purchase #2 $85.37   12.608%   $96.1334   $96.13   $96.15   $96.10  
  Purchase #3 $246.33   12.576%   $277.3085   $277.31   $277.30   $277.30  
  Purchase #4 $34.78   8.119%   $37.6038   $37.60   $37.60   $37.60  
  Purchase #5 $57.99   5.637%   $61.2589   $61.26   $61.25   $61.30  
  Purchase #6 $202.70   12.487%   $228.0111   $228.01   $228.00   $228.00  
  Purchase #7 $25.68   9.311%   $28.0711   $28.07   $28.05   $28.10  
  7 purchase totals = $867.27       $960.3206   $960.31   $960.30   $960.30