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 $58.44   4.573%   $61.1125   $61.11   $61.10   $61.10  
  Purchase #2 $245.32   3.644%   $254.2595   $254.26   $254.25   $254.30  
  Purchase #3 $8.45   5.711%   $8.9326   $8.93   $8.95   $8.90  
  Purchase #4 $79.26   12.690%   $89.3181   $89.32   $89.30   $89.30  
  Purchase #5 $93.58   4.203%   $97.5132   $97.51   $97.50   $97.50  
  Purchase #6 $153.68   6.619%   $163.8521   $163.85   $163.85   $163.90  
  Purchase #7 $98.47   6.349%   $104.7219   $104.72   $104.70   $104.70  
  7 purchase totals = $737.20       $779.7099   $779.70   $779.65   $779.70