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 $142.45   8.291%   $154.2605   $154.26   $154.25   $154.30  
  Purchase #2 $53.95   6.658%   $57.542   $57.54   $57.55   $57.50  
  Purchase #3 $78.58   7.817%   $84.7226   $84.72   $84.70   $84.70  
  Purchase #4 $160.35   9.310%   $175.2786   $175.28   $175.30   $175.30  
  Purchase #5 $232.74   11.296%   $259.0303   $259.03   $259.05   $259.00  
  Purchase #6 $63.39   8.281%   $68.6393   $68.64   $68.65   $68.60  
  Purchase #7 $243.41   12.362%   $273.5003   $273.50   $273.50   $273.50  
  7 purchase totals = $974.87       $1,072.9736   $1,072.97   $1,073.00   $1,072.90