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 $52.82   7.335%   $56.6943   $56.69   $56.70   $56.70  
  Purchase #2 $181.78   10.763%   $201.345   $201.35   $201.35   $201.30  
  Purchase #3 $216.96   4.144%   $225.9508   $225.95   $225.95   $226.00  
  Purchase #4 $94.54   4.536%   $98.8283   $98.83   $98.85   $98.80  
  Purchase #5 $172.76   6.229%   $183.5212   $183.52   $183.50   $183.50  
  Purchase #6 $24.60   11.364%   $27.3955   $27.40   $27.40   $27.40  
  Purchase #7 $153.42   6.114%   $162.8001   $162.80   $162.80   $162.80  
  7 purchase totals = $896.88       $956.5352   $956.54   $956.55   $956.50