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 $91.58   4.614%   $95.8055   $95.81   $95.80   $95.80  
  Purchase #2 $230.95   12.568%   $259.9758   $259.98   $260.00   $260.00  
  Purchase #3 $115.26   12.841%   $130.0605   $130.06   $130.05   $130.10  
  Purchase #4 $6.57   12.216%   $7.3726   $7.37   $7.35   $7.40  
  Purchase #5 $232.35   9.600%   $254.6556   $254.66   $254.65   $254.70  
  Purchase #6 $84.60   12.694%   $95.3391   $95.34   $95.35   $95.30  
  Purchase #7 $112.78   3.870%   $117.1446   $117.14   $117.15   $117.10  
  7 purchase totals = $874.09       $960.3537   $960.36   $960.35   $960.40