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 $52.27   4.421%   $54.5809   $54.58   $54.60   $54.60  
  Purchase #2 $8.60   11.508%   $9.5897   $9.59   $9.60   $9.60  
  Purchase #3 $114.73   4.696%   $120.1177   $120.12   $120.10   $120.10  
  Purchase #4 $189.52   13.696%   $215.4767   $215.48   $215.50   $215.50  
  Purchase #5 $201.55   3.121%   $207.8404   $207.84   $207.85   $207.80  
  Purchase #6 $95.38   11.401%   $106.2543   $106.25   $106.25   $106.30  
  Purchase #7 $249.31   8.751%   $271.1271   $271.13   $271.15   $271.10  
  7 purchase totals = $911.36       $984.9868   $984.99   $985.05   $985.00