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 $168.88   9.389%   $184.7361   $184.74   $184.75   $184.70  
  Purchase #2 $19.84   13.693%   $22.5567   $22.56   $22.55   $22.60  
  Purchase #3 $229.83   4.737%   $240.717   $240.72   $240.70   $240.70  
  Purchase #4 $232.92   9.351%   $254.7003   $254.70   $254.70   $254.70  
  Purchase #5 $98.81   11.812%   $110.4814   $110.48   $110.50   $110.50  
  Purchase #6 $156.37   7.127%   $167.5145   $167.51   $167.50   $167.50  
  Purchase #7 $75.85   4.485%   $79.2519   $79.25   $79.25   $79.30  
  7 purchase totals = $982.50       $1,059.9579   $1,059.96   $1,059.95   $1,060.00