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 $228.97   11.833%   $256.064   $256.06   $256.05   $256.10  
  Purchase #2 $191.86   10.608%   $212.2125   $212.21   $212.20   $212.20  
  Purchase #3 $59.52   13.574%   $67.5992   $67.60   $67.60   $67.60  
  Purchase #4 $26.68   4.729%   $27.9417   $27.94   $27.95   $27.90  
  Purchase #5 $191.74   7.612%   $206.3352   $206.34   $206.35   $206.30  
  Purchase #6 $157.86   9.301%   $172.5426   $172.54   $172.55   $172.50  
  Purchase #7 $229.51   4.701%   $240.2993   $240.30   $240.30   $240.30  
  7 purchase totals = $1,086.14       $1,182.9945   $1,182.99   $1,183.00   $1,182.90