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 $57.51   7.294%   $61.7048   $61.70   $61.70   $61.70  
  Purchase #2 $153.93   10.511%   $170.1096   $170.11   $170.10   $170.10  
  Purchase #3 $57.77   8.439%   $62.6452   $62.65   $62.65   $62.60  
  Purchase #4 $149.69   10.739%   $165.7652   $165.77   $165.75   $165.80  
  Purchase #5 $58.36   3.458%   $60.3781   $60.38   $60.40   $60.40  
  Purchase #6 $241.49   11.270%   $268.7059   $268.71   $268.70   $268.70  
  Purchase #7 $6.68   9.847%   $7.3378   $7.34   $7.35   $7.30  
  7 purchase totals = $725.43       $796.6466   $796.66   $796.65   $796.60