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 $87.39   10.451%   $96.5231   $96.52   $96.50   $96.50  
  Purchase #2 $155.89   12.118%   $174.7808   $174.78   $174.80   $174.80  
  Purchase #3 $206.41   8.118%   $223.1664   $223.17   $223.15   $223.20  
  Purchase #4 $55.25   8.376%   $59.8777   $59.88   $59.90   $59.90  
  Purchase #5 $142.72   13.205%   $161.5662   $161.57   $161.55   $161.60  
  Purchase #6 $51.26   4.697%   $53.6677   $53.67   $53.65   $53.70  
  Purchase #7 $212.73   9.248%   $232.4033   $232.40   $232.40   $232.40  
  7 purchase totals = $911.65       $1,001.9852   $1,001.99   $1,001.95   $1,002.10