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 $23.81   3.349%   $24.6074   $24.61   $24.60   $24.60  
  Purchase #2 $232.47   6.199%   $246.8808   $246.88   $246.90   $246.90  
  Purchase #3 $156.71   7.831%   $168.982   $168.98   $169.00   $169.00  
  Purchase #4 $120.48   7.526%   $129.5473   $129.55   $129.55   $129.50  
  Purchase #5 $25.65   7.585%   $27.5956   $27.60   $27.60   $27.60  
  Purchase #6 $238.79   4.273%   $248.9935   $248.99   $249.00   $249.00  
  Purchase #7 $198.87   3.470%   $205.7708   $205.77   $205.75   $205.80  
  7 purchase totals = $996.78       $1,052.3774   $1,052.38   $1,052.40   $1,052.40