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 $185.73   5.572%   $196.0789   $196.08   $196.10   $196.10  
  Purchase #2 $204.49   8.847%   $222.5812   $222.58   $222.60   $222.60  
  Purchase #3 $119.72   5.498%   $126.3022   $126.30   $126.30   $126.30  
  Purchase #4 $41.63   12.714%   $46.9228   $46.92   $46.90   $46.90  
  Purchase #5 $58.68   11.489%   $65.4217   $65.42   $65.40   $65.40  
  Purchase #6 $101.72   11.653%   $113.5734   $113.57   $113.55   $113.60  
  Purchase #7 $211.67   7.619%   $227.7971   $227.80   $227.80   $227.80  
  7 purchase totals = $923.64       $998.6773   $998.67   $998.65   $998.70