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 $69.80   9.548%   $76.4645   $76.46   $76.45   $76.50  
  Purchase #2 $95.64   11.574%   $106.7094   $106.71   $106.70   $106.70  
  Purchase #3 $150.52   11.598%   $167.9773   $167.98   $168.00   $168.00  
  Purchase #4 $202.68   4.787%   $212.3823   $212.38   $212.40   $212.40  
  Purchase #5 $235.92   6.244%   $250.6508   $250.65   $250.65   $250.70  
  Purchase #6 $37.53   13.443%   $42.5752   $42.58   $42.60   $42.60  
  Purchase #7 $60.99   8.551%   $66.2053   $66.21   $66.20   $66.20  
  7 purchase totals = $853.08       $922.9648   $922.97   $923.00   $923.10