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 $56.27   3.737%   $58.3728   $58.37   $58.35   $58.40  
  Purchase #2 $223.81   11.837%   $250.3024   $250.30   $250.30   $250.30  
  Purchase #3 $102.33   7.749%   $110.2596   $110.26   $110.25   $110.30  
  Purchase #4 $153.62   7.422%   $165.0217   $165.02   $165.00   $165.00  
  Purchase #5 $131.44   8.864%   $143.0908   $143.09   $143.10   $143.10  
  Purchase #6 $159.88   6.753%   $170.6767   $170.68   $170.70   $170.70  
  Purchase #7 $132.94   6.573%   $141.6781   $141.68   $141.70   $141.70  
  7 purchase totals = $960.29       $1,039.4021   $1,039.40   $1,039.40   $1,039.50