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 $13.44   7.433%   $14.439   $14.44   $14.45   $14.40  
  Purchase #2 $143.61   8.534%   $155.8657   $155.87   $155.85   $155.90  
  Purchase #3 $103.30   7.310%   $110.8512   $110.85   $110.85   $110.90  
  Purchase #4 $222.64   7.814%   $240.0371   $240.04   $240.05   $240.00  
  Purchase #5 $98.40   7.415%   $105.6964   $105.70   $105.70   $105.70  
  Purchase #6 $95.51   12.500%   $107.4488   $107.45   $107.45   $107.40  
  Purchase #7 $94.55   10.570%   $104.5439   $104.54   $104.55   $104.50  
  7 purchase totals = $771.45       $838.8821   $838.89   $838.90   $838.80