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 $87.46   7.569%   $94.0798   $94.08   $94.10   $94.10  
  Purchase #2 $16.58   6.760%   $17.7008   $17.70   $17.70   $17.70  
  Purchase #3 $31.44   10.257%   $34.6648   $34.66   $34.65   $34.70  
  Purchase #4 $104.82   13.527%   $118.999   $119.00   $119.00   $119.00  
  Purchase #5 $45.46   3.874%   $47.2211   $47.22   $47.20   $47.20  
  Purchase #6 $202.64   8.483%   $219.83   $219.83   $219.85   $219.80  
  Purchase #7 $147.93   13.227%   $167.4967   $167.50   $167.50   $167.50  
  7 purchase totals = $636.33       $699.9922   $699.99   $700.00   $700.00