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 $148.82   13.320%   $168.6428   $168.64   $168.65   $168.60  
  Purchase #2 $195.80   13.306%   $221.8531   $221.85   $221.85   $221.90  
  Purchase #3 $51.54   10.535%   $56.9697   $56.97   $56.95   $57.00  
  Purchase #4 $244.40   13.161%   $276.5655   $276.57   $276.55   $276.60  
  Purchase #5 $161.41   6.334%   $171.6337   $171.63   $171.65   $171.60  
  Purchase #6 $70.67   13.586%   $80.2712   $80.27   $80.25   $80.30  
  Purchase #7 $157.50   5.815%   $166.6586   $166.66   $166.65   $166.70  
  7 purchase totals = $1,030.14       $1,142.5946   $1,142.59   $1,142.55   $1,142.70