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 $214.58   12.632%   $241.6857   $241.69   $241.70   $241.70  
  Purchase #2 $53.88   5.364%   $56.7701   $56.77   $56.75   $56.80  
  Purchase #3 $107.45   7.408%   $115.4099   $115.41   $115.40   $115.40  
  Purchase #4 $202.40   9.563%   $221.7555   $221.76   $221.75   $221.80  
  Purchase #5 $52.98   6.759%   $56.5609   $56.56   $56.55   $56.60  
  Purchase #6 $95.85   12.491%   $107.8226   $107.82   $107.80   $107.80  
  Purchase #7 $23.33   5.115%   $24.5233   $24.52   $24.50   $24.50  
  7 purchase totals = $750.47       $824.5280   $824.53   $824.45   $824.60