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 $169.52   8.807%   $184.4496   $184.45   $184.45   $184.40  
  Purchase #2 $226.56   6.807%   $241.9819   $241.98   $242.00   $242.00  
  Purchase #3 $46.84   13.850%   $53.3273   $53.33   $53.35   $53.30  
  Purchase #4 $101.32   12.803%   $114.292   $114.29   $114.30   $114.30  
  Purchase #5 $115.64   3.771%   $120.0008   $120.00   $120.00   $120.00  
  Purchase #6 $157.94   12.704%   $178.0047   $178.00   $178.00   $178.00  
  Purchase #7 $123.83   7.641%   $133.2919   $133.29   $133.30   $133.30  
  7 purchase totals = $941.65       $1,025.3482   $1,025.34   $1,025.40   $1,025.30