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 $173.32   13.860%   $197.3422   $197.34   $197.35   $197.30  
  Purchase #2 $71.88   10.677%   $79.5546   $79.55   $79.55   $79.60  
  Purchase #3 $127.59   8.449%   $138.3701   $138.37   $138.35   $138.40  
  Purchase #4 $111.25   4.720%   $116.501   $116.50   $116.50   $116.50  
  Purchase #5 $192.97   13.670%   $219.349   $219.35   $219.35   $219.30  
  Purchase #6 $211.31   11.351%   $235.2958   $235.30   $235.30   $235.30  
  Purchase #7 $32.74   10.133%   $36.0575   $36.06   $36.05   $36.10  
  7 purchase totals = $921.06       $1,022.4702   $1,022.47   $1,022.45   $1,022.50