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 $62.25   10.109%   $68.5429   $68.54   $68.55   $68.50  
  Purchase #2 $156.42   8.853%   $170.2679   $170.27   $170.25   $170.30  
  Purchase #3 $205.77   3.309%   $212.5789   $212.58   $212.60   $212.60  
  Purchase #4 $180.99   11.676%   $202.1224   $202.12   $202.10   $202.10  
  Purchase #5 $154.65   6.632%   $164.9064   $164.91   $164.90   $164.90  
  Purchase #6 $22.56   12.250%   $25.3236   $25.32   $25.30   $25.30  
  Purchase #7 $88.90   12.436%   $99.9556   $99.96   $99.95   $100.00  
  7 purchase totals = $871.54       $943.6977   $943.70   $943.65   $943.70