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 $60.58   4.596%   $63.3643   $63.36   $63.35   $63.40  
  Purchase #2 $147.90   5.465%   $155.9827   $155.98   $156.00   $156.00  
  Purchase #3 $227.26   6.226%   $241.4092   $241.41   $241.40   $241.40  
  Purchase #4 $200.53   6.540%   $213.6447   $213.64   $213.65   $213.60  
  Purchase #5 $10.35   9.464%   $11.3295   $11.33   $11.35   $11.30  
  Purchase #6 $91.86   12.400%   $103.2506   $103.25   $103.25   $103.30  
  Purchase #7 $246.38   6.762%   $263.0402   $263.04   $263.05   $263.00  
  7 purchase totals = $984.86       $1,052.0212   $1,052.01   $1,052.05   $1,052.00