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 $30.43   13.763%   $34.6181   $34.62   $34.60   $34.60  
  Purchase #2 $190.43   6.661%   $203.1145   $203.11   $203.10   $203.10  
  Purchase #3 $64.72   5.661%   $68.3838   $68.38   $68.40   $68.40  
  Purchase #4 $237.30   11.604%   $264.8363   $264.84   $264.85   $264.80  
  Purchase #5 $184.90   11.599%   $206.3466   $206.35   $206.35   $206.30  
  Purchase #6 $152.61   7.157%   $163.5323   $163.53   $163.55   $163.50  
  Purchase #7 $68.38   8.523%   $74.208   $74.21   $74.20   $74.20  
  7 purchase totals = $928.77       $1,015.0396   $1,015.04   $1,015.05   $1,014.90