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 $67.41   13.273%   $76.3573   $76.36   $76.35   $76.40  
  Purchase #2 $174.59   11.453%   $194.5858   $194.59   $194.60   $194.60  
  Purchase #3 $126.62   9.338%   $138.4438   $138.44   $138.45   $138.40  
  Purchase #4 $196.97   12.447%   $221.4869   $221.49   $221.50   $221.50  
  Purchase #5 $204.58   7.168%   $219.2443   $219.24   $219.25   $219.20  
  Purchase #6 $186.88   10.236%   $206.009   $206.01   $206.00   $206.00  
  Purchase #7 $201.32   5.504%   $212.4007   $212.40   $212.40   $212.40  
  7 purchase totals = $1,158.37       $1,268.5278   $1,268.53   $1,268.55   $1,268.50