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 $123.95   4.849%   $129.9603   $129.96   $129.95   $130.00  
  Purchase #2 $241.97   3.691%   $250.9011   $250.90   $250.90   $250.90  
  Purchase #3 $59.98   11.759%   $67.033   $67.03   $67.05   $67.00  
  Purchase #4 $90.74   7.531%   $97.5736   $97.57   $97.55   $97.60  
  Purchase #5 $218.47   13.775%   $248.5642   $248.56   $248.55   $248.60  
  Purchase #6 $190.27   11.589%   $212.3204   $212.32   $212.30   $212.30  
  Purchase #7 $40.49   13.201%   $45.8351   $45.84   $45.85   $45.80  
  7 purchase totals = $965.87       $1,052.1877   $1,052.18   $1,052.15   $1,052.20