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 $197.65   8.807%   $215.057   $215.06   $215.05   $215.10  
  Purchase #2 $75.44   13.162%   $85.3694   $85.37   $85.35   $85.40  
  Purchase #3 $61.58   11.648%   $68.7528   $68.75   $68.75   $68.80  
  Purchase #4 $22.98   6.607%   $24.4983   $24.50   $24.50   $24.50  
  Purchase #5 $52.34   6.466%   $55.7243   $55.72   $55.70   $55.70  
  Purchase #6 $160.50   6.829%   $171.4605   $171.46   $171.45   $171.50  
  Purchase #7 $69.50   4.566%   $72.6734   $72.67   $72.65   $72.70  
  7 purchase totals = $639.99       $693.5357   $693.53   $693.45   $693.70