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 $151.43   11.831%   $169.3457   $169.35   $169.35   $169.30  
  Purchase #2 $209.54   12.465%   $235.6592   $235.66   $235.65   $235.70  
  Purchase #3 $9.30   11.635%   $10.3821   $10.38   $10.40   $10.40  
  Purchase #4 $105.85   10.435%   $116.8954   $116.90   $116.90   $116.90  
  Purchase #5 $188.61   7.249%   $202.2823   $202.28   $202.30   $202.30  
  Purchase #6 $47.77   11.872%   $53.4413   $53.44   $53.45   $53.40  
  Purchase #7 $216.74   6.135%   $230.037   $230.04   $230.05   $230.00  
  7 purchase totals = $929.24       $1,018.0430   $1,018.05   $1,018.10   $1,018.00