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 $192.80   9.800%   $211.6944   $211.69   $211.70   $211.70  
  Purchase #2 $60.47   13.173%   $68.4357   $68.44   $68.45   $68.40  
  Purchase #3 $91.58   11.525%   $102.1346   $102.13   $102.15   $102.10  
  Purchase #4 $145.34   9.786%   $159.563   $159.56   $159.55   $159.60  
  Purchase #5 $243.42   5.664%   $257.2073   $257.21   $257.20   $257.20  
  Purchase #6 $120.60   10.713%   $133.5199   $133.52   $133.50   $133.50  
  Purchase #7 $84.54   7.106%   $90.5474   $90.55   $90.55   $90.50  
  7 purchase totals = $938.75       $1,023.1023   $1,023.10   $1,023.10   $1,023.00