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 $50.57   10.706%   $55.984   $55.98   $56.00   $56.00  
  Purchase #2 $235.64   4.718%   $246.7575   $246.76   $246.75   $246.80  
  Purchase #3 $102.40   7.728%   $110.3135   $110.31   $110.30   $110.30  
  Purchase #4 $233.25   3.352%   $241.0685   $241.07   $241.05   $241.10  
  Purchase #5 $220.59   12.234%   $247.577   $247.58   $247.60   $247.60  
  Purchase #6 $244.42   13.265%   $276.8423   $276.84   $276.85   $276.80  
  Purchase #7 $86.36   3.599%   $89.4681   $89.47   $89.45   $89.50  
  7 purchase totals = $1,173.23       $1,268.0109   $1,268.01   $1,268.00   $1,268.10