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 $62.38   11.528%   $69.5712   $69.57   $69.55   $69.60  
  Purchase #2 $137.87   5.146%   $144.9648   $144.96   $144.95   $145.00  
  Purchase #3 $36.81   11.656%   $41.1006   $41.10   $41.10   $41.10  
  Purchase #4 $249.85   13.535%   $283.6672   $283.67   $283.65   $283.70  
  Purchase #5 $176.88   4.136%   $184.1958   $184.20   $184.20   $184.20  
  Purchase #6 $57.89   9.787%   $63.5557   $63.56   $63.55   $63.60  
  Purchase #7 $120.83   9.245%   $132.0007   $132.00   $132.00   $132.00  
  7 purchase totals = $842.51       $919.0560   $919.06   $919.00   $919.20