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 $54.88   3.390%   $56.7404   $56.74   $56.75   $56.70  
  Purchase #2 $10.69   6.328%   $11.3665   $11.37   $11.35   $11.40  
  Purchase #3 $87.55   8.242%   $94.7659   $94.77   $94.75   $94.80  
  Purchase #4 $227.70   7.731%   $245.3035   $245.30   $245.30   $245.30  
  Purchase #5 $184.58   4.774%   $193.3918   $193.39   $193.40   $193.40  
  Purchase #6 $212.72   12.342%   $238.9739   $238.97   $238.95   $239.00  
  Purchase #7 $207.36   9.866%   $227.8181   $227.82   $227.80   $227.80  
  7 purchase totals = $985.48       $1,068.3601   $1,068.36   $1,068.30   $1,068.40