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 $88.33   8.650%   $95.9705   $95.97   $95.95   $96.00  
  Purchase #2 $53.31   9.132%   $58.1783   $58.18   $58.20   $58.20  
  Purchase #3 $231.37   8.135%   $250.1919   $250.19   $250.20   $250.20  
  Purchase #4 $14.42   11.646%   $16.0994   $16.10   $16.10   $16.10  
  Purchase #5 $5.36   4.248%   $5.5877   $5.59   $5.60   $5.60  
  Purchase #6 $123.88   4.277%   $129.1783   $129.18   $129.20   $129.20  
  Purchase #7 $52.47   9.526%   $57.4683   $57.47   $57.45   $57.50  
  7 purchase totals = $569.14       $612.6744   $612.68   $612.70   $612.80